From the first to the fifteenth century
A huge lighthouse was built by Claudius between the two moles of his harbour. Ancient authors (Suetonius, Cassius Dio) tell us that the lighthouse was on top of an island, an isolated mole. They also state that part of the foundation of the lighthouse consisted of a huge ship, that had been used by Caligula to carry an obelisk from Egypt to Rome. Apparently it was used as a caisson. The building process must have been similar to that of the harbour at Centumcellae, not far away, during the reign of Trajan. It is described as follows by Pliny the Younger:
"I was delighted to be summoned by the Emperor [Trajanus] to act as his assessor at Centum Cellae [Civitavecchia], where I am now." [...] "The house is really beautiful: it is surrounded by green fields and faces the sea-shore, where a natural bay is being converted with all speed into a harbour. The left arm has already been reinforced by a solid mole and the right is in process of construction. At the entrance to the harbour an island is rising out of the water to act as a breakwater when the wind blows inland, and so give a safe passage to ships entering from either side. Its construction is well worth seeing. Huge stones are brought by large barges and thrown out one on top of another facing the harbour; their weight keeps them in position and the pile gradually rises in a sort of rampart. A hump of rocks can already be seen sticking up, which breaks the waves beating against it and tosses them high into the air with a resounding crash, so that the sea all round is white with foam. Later on piers will be built on the stone foundation, and as time goes on it will look like a natural island. The harbour will be called after its maker, and is in fact already known by his name; and it will save countless lives by providing a haven on this long stretch of harbourless coast."
Suetonius tells us that Claudius "built upon piles a very lofty tower, in imitation of the Pharos at Alexandria (altissimam turrem in exemplum Alexandrini Phari), on which lights were burnt to direct mariners in the night" (Suetonius, Claudius XX), It could also be called Pharos, as could other lighthouses (see e.g. Herodianus IV,2,8). It is depicted on many mosaics, in drawings, on reliefs, on funerary slabs, on coins, and on the Tabula Peutingeriana.
The lighthouse seems to have been restored by Antoninus Pius: Phari restitutio (SHA 8, 2-3; the context suggests that the lighthouse of Portus is meant, because it is mentioned in a list of work that took place in Italy only). In the years 334-345 AD Lucius Crepereius Madalianus is consul(aris) molium phari at(que) purgaturae, i.e. responsible for the maintenance of the moles and the lighthouse, and for dredging in the harbour. Here is what we read in an inscription that was found near the hexagon by Guido Calza (Calza 1925; Thylander B336):
BONITATI POLLENTI LVCIO
CREPEREIO MADALIANO V(iro) C(larissimo)
PRAEF(ecto) ANN(onae) CVM IVRE GLADII
COMITI FLAVIALI CORR(ectori) FLAM(iniae)
ET PICENI LEG(ato) PRO PRAETORE PROV(inciae)
ASIAE LEG(ato) PROV(inciae) AFRICAE CONSVLA(ri)
AED(ium) SACRAR(um) CONSVL(ari) MOLIVM PHARI
AT(que) PVRGATVRAE QUAEST(ori) CANDID(ato)
PRAET(ori) CONSVLI OB MVLTA IN SE EIVS
TESTIMONIA ORDO ET POPVLVS (civitatis)
FL(aviae) CONSTANTINIANAE PORTVENSES
STATVAM PVBLICAE PONENDVM CENSVERVNT
The Codex Theodosianus (XIV.6.3.1-8) mentions the lighthouse in 365 AD.
Documents from 1018 and 1049 mention two towers in Portus, presumably the Claudian and Trajanic lighthouses. One is called Cocuzina or Cucuzuba / Cucuzuta, the other Molon or Montone. We also hear of a fundus Bacatus, a name apparently derived from the Claudian lighthouse (Baccha = Specula = Pharus). On August 25, 1190 Richard Coeur de Lion visited Ostia, and we hear this: Praeteriit ... locum dictum Le Far de Rume. Et postea intravit Tyberim; ad cuius introitum est turris pulcerrima sed solitaria ("He passed a place called Le Far de Rume. And after that he entered the mouth of the Tiber, at the entrance of which is a very beautiful but solitary tower"). Meiggs suggests that he saw Tor Boacciana, which was perhaps a small lighthouse at the mouth of the Ostian branch of the Tiber. This is what the text suggests, but can that simple tower really be called a very beautiful tower, or was this the lighthouse of Portus? Remains of the lighthouse could still be seen in the 15th century. In the book De Roma instaurata, written 1444-1446, Flavio Biondo wrote: "Di questa torre ne veggiamo, insino ad hoggi una buona parte in pie, se non che ne sono stati tolti i marmi, de quali ella era incrustata" (translation by Lucio Fauno, Venezia 1558, 41). Note that according to Flavio Biondo the tower was decorated with marble. In his Commentaria rerum memorabilium Pius II Piccolomini wrote (May 1463): "Turris adhuc extant vestigia, quae procul in mari cernuntur." (edition Frankfurt 1614, 301) ("There are still traces of this tower which can be seen from far out at sea."). In 1483 Sixtus IV (Francesco della Rovere) visited Portus "dove si vedono ancora i muri vetustissimi della città di Porto, molto diruti, e la torre del Faro, tanto che ancora oggi essa conserva lo stesso nome" (Iacopo Gherardi, Il Diario di Roma, in Muratori, Rerum Italicarum Scriptores Vol. 23, part 3, 3-4). After 1483 there are no further references to the lighthouse. Perhaps the last remains were demolished soon afterwards.
The sunset gives us an impression of what the lighthouse of Claudius looked like, as seen from Ostia.
Photo: Parco Archeologico di Ostia.
The discovery of the lighthouse
In the years 2001-2007 the Soprintendenza has done a lot of work in the west part of the harbour of Claudius, necessitated by building activity in Fiumicino and at the airport Leonardo da Vinci. The work consisted of both excavations and drillings. This research has led to the localization of the western part of the two moles of the harbour and of the lighthouse-island.
In the fifteenth century remains could still be seen in the sea. The moles and the island are depicted on several drawings and paintings from the sixteenth and seventeenth century, with the lighthouse on an island in front of the passage between the moles. In the nineteenth century the remains were covered by earth, because the coastline kept moving to the west. Reconstructions in the nineteenth century are much different. The lighthouse is no longer on an island, but on a mole.
Through the drillings remains were found of the western end of the southern and northern mole, and of the lighthouse-island, with passages to the north and south. This means that the older reconstructions were correct. The remains are beyond Viale di Coccia di Morto, much further to the west than had been expected in the twentieth century. The remains (tufa, basalt, bricks, sherds) are at a great depth (-3 to -15.5 metres). The size of the basin of Claudius was more than 200 hectares. The northern mole was 1.600 metres long, the southern one c. 1.320. The island was indeed not between the end of the two moles, but a little further to the west.
Plan with the two moles and the location of the lighthouse (Morelli - Marinucci - Arnoldus-Huyzendveld 2011, fig. 4.10).
Lighthouse.kmz for Google Earth (Antonia Arnoldus-Huyzendveld).
The drillings compared with an old fresco (Antonia Arnoldus-Huyzendveld).
The location of the lighthouse-island (photograph 2007, Jan Theo Bakker).
The location of the lighthouse-island (photograph 2007, Jan Theo Bakker).
Building activity on the passage to the south of the lighthouse-island (photograph 2007, Jan Theo Bakker).
Source: Cinzia Morelli - Alfredo Marinucci - Antonia Arnoldus-Huyzendveld, "Porto di Claudio: nuove scoperte", in "Portus and its hinterland: recent archaeological research" (edited by Simon Keay and Lidia Paroli), London 2011, 47-65.
The lighthouse of Alexandria
Various ancient authors provide information about the lighthouse of Alexandria: Diodorus Siculus, Strabo, Plinius Senior (XXXVI,18/83), Lucianus (Hippias II), Posidippos, Flavius Josephus and Eusebius. It is depicted on coins and mosaics (Libya, 6th century, identified by a text; San Marco, Venice, 12th century). There are also descriptions by Arab travelers, such as El-Andalusi (1166 AD).
The lighthouse received its name from the island on top of which it was built: Pharos. The island was dedicated to the marine deity Proteus. The tower was built in the early third century BC, probably by the architect Sostratos, who worked at the court of Ptolemaios I. It was added to the list of the seven wonders of the world in the sixth century. It was damaged and destroyed by earthquakes in the 10th and 14th century.
The dedicatory inscription of huge lead letters mentioned "saviour gods for sailors". Some have suggested that the tower was dedicated to Poseidon and Zeus Soter (a statue of the god, with sceptre and bolt of lightning, seems to have been on top). Others have suggested the Dioscures or Ptolemaios I and his wife Berenike. On coins the tower is depicted together with Isis Pharia. A colossal statue of the goddess was found in the sea. She may have had a temple on the island. Huge statues of Ptolemaic kings and queens were found in the sea not long ago by Jean-Yves Empereur. There were statues of Tritons with trumpets on the first level.
The desciption by El-Andalusi is confusing and contains clear errors. He mentions a podium and a cylindrical heart, a first square level, a second octagonal level and a third cylindrical level. The tower would have been 96.99 m. high, and if the podium and statue of Zeus are added, it had a total height of 117 m. According to Flavius Josephus it could be seen from a distance of 55 km. Strabo says that is was made of white stone, possibly limestone. Coins and mosaics show the side with the main entrance. It was high and arched. Above it was a round window and it was flanked by slit windows. The second level had a large rectangular door. There were balustrades on top of the first and second level, and more slit windows in the second and third. Visitors of the tower reported that donkeys took fuel (wood or oil?) to the top.
The lighthouse of Alexandria on a coin of Domitianus.
Testaguzza 1970, p. 124.
- P. Clayton - M. Price, The Seven Wonders of the Ancient World, 1990.
- J. and E. Romer, The Seven Wonders of the World, a History of Modern Imagination, 1995.
- P. Jordan, The Seven Wonders of the Ancient World, 2002.
- H. Thiersch, Pharos, Antike, Islam und Occident - Ein Beitrag zur Architekturgeschichte, 1909.
Ancient depictions of the lighthouse
01 Mosaic in the House of the Harbour Mosaic (I,XIV,2).
The lighthouse has six storeys, including the cylinder with the fire. Lines on the bottom storey suggest the use of large blocks of stone. In the centre of this storey is a large, arched opening. In the centre of the three next storeys is a rectangular door or window. The lowest door or window is flanked by two vertical lines, possibly slit windows. The height of the lower storeys decreases from bottom to top, the three highest storeys have the same height.
02 Mosaic in statio 3 on the Square of the Corporations (II,VII,4).
Only a small part of the lighthouse has been preserved: the top storey i.e. the cylinder with the fire. It has two white stones. Below is part of the penultimate storey, seen from above.
03 Mosaic in statio 22 on the Square of the Corporations (II,VII,4).
The lighthouse has five storeys, including the cylinder. In the centre of the bottom storey is a large, arched opening. The next storey has two doors at the sides. The next one has two windows at the sides. The first and second storey are higher than the second and fourth.
04 Mosaic in statio 23 on the Square of the Corporations (II,VII,4).
The lighthouse has three storeys, including the cylinder. In the centre of the two lowest storeys is a large, arched opening, the lower one much bigger than the other. The lower one is flanked by two white lines, possibly slit windows. The first storey is much higher than the second. There are many white stones in the cylinder.
05 Mosaic in statio 26 on the Square of the Corporations (II,VII,4).
The is a depiction of the upper part of the lighthouse, seen from above. On the cylinder with the fire is a white rectangle with a few white stones towards the sides. In the centre of the storey below it is a large, arched opening. White lines suggest a railing.
06 Mosaic in statio 35 on the Square of the Corporations (II,VII,4).
We see four storeys, including the cylinder with the fire. The bottom one is very high and wide.
07 Mosaic in statio 46 on the Square of the Corporations (II,VII,4).
The lighthouse has four storeys, including the cylinder. White lines on the lower three storeys suggest the use of large blocks of stone. In the centre of all storeys is a large, arched opening. Both the storeys and the openings are getting smaller towards the top.
08 Mosaic in statio 49 on the Square of the Corporations (II,VII,4).
The lighthouse has four storeys, including the cylinder. In the centre of the bottom storey is a large, arched opening. The threshold is at quite a distance from the bottom of the tower. In the centre of the next storey are two doors or windows. In the centre of the next one is a door. The bottom storey is the highest and widest one.
09 Mosaic in the Baths of the Lighthouse (IV,II,1).
The lighthouse has six stories, including the cylinder. White lines on the lower five storeys suggest the use of large blocks of stone. In the centre of these storeys are large, arched openings. The interior of the lower three is black, that of the other two white. Below the first opening is a black rectangle. The storeys and openings are getting smaller towards the top, with the exception of the fourth one.
10 Mosaic in the Isola Sacra necropolis, tomb 43.
The lighthouse has four storeys, including the cylinder. In the centre of the bottom storey is a large, arched opening. In the upper part of the first three storeys are many vertical white lines, presumably slit windows. The first storey is by far the largest.
11 Mosaic in the Imperial Palace of Ostia, courtyard 73.
This is a depiction of the upper part of the lighthouse. The fire is flanked by two objects looking like spoons. The fire in between looks like a balloon.
12 Relief of a ship approaching the lighthouse.
Three storeys can be seen. In the centre of each storey is a large, arched opening, the middle one beginning quite high, as if it is a window. The first two storeys and arches are much higher than the third one.
13 Relief on a sarcophagus of a ship approaching the lighthouse, from the Isola Sacra necropolis, tomb 90.
The lighthouse has four storeys, including the cylinder. The first three have vertical lines, possibly slit windows. The storeys are getting lower towards the top.
14 Relief of the lighthouse, on the Torlonia Relief, from Portus. Also a female figure with the lighthouse on her head in the upper left corner.
a. The lighthouse on the head of the female figure (top left) has four storeys, including the cylinder. In the centre of the first three storeys are doors or windows. One side of the first two storeys can be seen. The figure is the presonification of Portus.
b. The lighthouse can be seen further to the right, largely covered by a passing ship. The fire is burning in the cylinder. Next to it is a statue of a figure holding a sceptre or lance, possibly Claudius or Nero. There seem to be four storeys below it. In the right part of the first storey is a large, arched opening. In the interior opus reticulatum seems visible. There seems to be a small staircase to the right. The first storey is the highest. The next one is very low. Towards the right is a small window. The next two storeys have a door, that is not in the centre. The right side of the fourth storey can be seen, with a small window.
15 Relief of the lighthouse on a travertine block, probably from a tomb to the south of Ostia, now outside the museum in Ostia. Photograph: Giovanni Lattanzi, www.archart.it. Reproduced with permission.
The lighthouse has four storeys, including the cylinder. In the centre of the first storey is a large, arched opening. The storeys are getting lower towards the top.
16 Graffito from Ostia.
A simple drawing of the lighthouse with three storeys, including the cylinder. The first storey is lower than the second one.
17 Graffito from Ostia.
A simple drawing of the lighthouse with three storeys, including the cylinder. The first storey is the highest one.
18 Graffito from Ostia.
A drawing of the lighthouse with three storeys, that are very high and slender. There is a window in the centre of the first and third storey. There may be a few lines to indicate the fire. Probably the lighthouse of Alexandria.
19 Graffito from Ostia (next to Trajan's column).
A very simple drawing of the lighthouse with three storeys, including the cylinder. There seem to be windows in the centre of the first and second storey. The first storey is the highest one.
20 Painting from the so-called Capitaneria in the harbour of Claudius: two masks of winds flanking the lighthouse (Testaguzza 1970, p. 125); colour photo (Parco Archeologico di Ostia).
21 Coin of Antoninus Pius, with depictions of a grain measure, Annona (personification of the grain supply) holding a tessera frumentaria and a rudder, and the lighthouse. Text: ANNONA AVG FELIX SC (Meiggs 1973, Pl. XVIII).
The lighthouse has four storeys, including the cylinder. Lines on the first three storeys suggest the use of large blocks of stone. The first storey is the highest one.
22 Coin of Commodus, with depictions of ships (one with Jupiter Serapis), two men sacrificing (one of which is the Emperor), and the lighthouse. Text: VOTIS FELICIBVS (Meiggs 1973, Pl. XVIII).
The lighthouse seems to have three storeys, including the cylinder. Lines on the first two storeys suggest the use of large blocks of stone, or indicate doors or windows.
23 Funerary slabs with depictions of the lighthouse (Stuhlfauth 1938, figs. 5, 6, 7).
Abb. 5. The lighthouse has four storeys, including the cylinder. They are getting lower towards the top.
Abb. 6. The lighthouse has four storeys, including the cylinder. They are getting lower towards the top. In the centre of the first three storeys are large, arched openings.
Abb. 7. The lighthouse has four storeys, including the cylinder. The first one is the highest one. In the centre of the first storey is a large, arched opening.
24 Drawing of the lighthouse on the Tabula Peutingeriana.
The lighthouse has three or four storeys, including the cylinder. The two storeys below the cylinder have three doors.
25 Tessera with depiction of the lighthouse and the text ANT.
Added in 2017. See also cointalk.com.
26 Sarcophagus with depiction of a female figure to the left of Annona. With her left hand she supports a lighthouse. The figure has been interpreted as the personification of Portus. Aquari sarcophagus (Annona sarcophagus; 270-280 AD).
Added in 2017. See also vroma.org (Ann Raia, 2009).
27 Relief with depiction of two ships and the lighthouse. Reused in the cathedral ("duomo") of Pisa.
Added in 2017. Photo: Massimiliano David.
28 Relief with depiction of two Genii, each holding a cornucopiae and a lighthouse. Below that a snake and the Greek text "Good speed to the (Alexandrian grain) fleet" (euploia toi stoloi). On the panel in between Alpha Omega and Chi Rho. Found in 1797 in Portus, now in the Vatican Museums.
Added in 2020. Photos: EAGLE, EDR120079.
29 Relief with depiction of a ship with a dolphin, the lighthouse and the personification of Portus with a bull. Ostia inv. nr. 49132.
Added in 2020. Photo: Karivieri 2020, p. 61 fig. 2.
The height of the lighthouse
The ancient authors do not give us an indication about the height of the lighthouse. It seems that the lighthouse in Alexandria was almost 120 metres high (with a foundation of 30x30 metres). There are several reasons to think that the lighthouse of Portus was a bit higher. First of all, Suetonius establishes a clear relation between the two towers when he says that the lighthouse of Portus was an altissimam turrem in exemplum Alexandrini Phari (Suetonius, Claudius XX). The many depictions of the lighthouse (especially the graffiti) suggest, that it was an impressive monument. Finally, it is not unreasonable to think that Claudius wanted to stipulate the supremacy of Rome. The lighthouse of Alexandria was famous because it was the highest building in the world. A Roman Emperor could hardly tolerate that the main lighthouse of Portus and therefore of Rome would be lower. Egypt was "just" a province, supplying grain to the capital. Boyce may well be right when he suggests, that the sinking of the ship that had been used for the transport of an obelisk was not only a technical operation, but also a symbolical deed (Boyce 1958, p. 77).
If the tower was only 50 metres high it could be seen in Rome - and it surely could. If it was 120 metres high it could be seen at a distance of at least 40 kilometres. The next lighthouse to the south may have been in Antium, almost 50 kilometres away.
The shape, number and height of the storeys
According to Stuhlfauth the lighthouse probably had four storeys: the lower three square or rectangular, the upper one cylindrical. The shapes can be seen clearly on several ancient depictions (nrs. 2, 5, 14a, 14b).
On the ancient depictions we see three, four, five and six storeys. I am inclined to think that there were six storeys. This number is seen on two mosaics. The first is in the Baths of the Lighthouse (nr. 9). This mosaic is of good quality and one might argue that the tower was stretched for artistic reasons. However, the other mosaic showing six storeys, in the House of the Harbour Mosaic (nr. 1), is much simpler, and here simplification would be expected, rather than stretching.
On most depictions the storeys become lower towards the top. We might think of storeys that were 40 - 30 - 20 - 15 - 10 - 5 metres high. The first storey seems to have been very wide and high (nrs. 4, 8, 10, 16, 17, 19, 23.7).
The nickname of the campanile of San Paolo fuori Le Mura, built in 1860, is "il faro". The model for it was the lighthouse of Portus.
The only direct evidence for the materials that were used comes from the drillings, for the most part remains of the foundation of the island on which the tower rested. They were found at a great depth, up to -15 metres, the ancient seafloor. The finds included basalt, "tufo lionato" (tufa turned black by water and called lapis ruber), and some marble and granite (oral communication, Antonia Arnoldus-Huyzendveld).
Large basalt blacks were used for a mole near Monte Arena, and Pliny the Younger mentions the dumping of large stone blocks at Centumcellae, to create an island (see above). Pliny the Elder makes a remarkable statement about the obelisk-ship: "The caissons made of cement were erected in its hull at Pozzuoli; whereupon it was towed to Ostia and sunk there by order of the emperor, so to contribute to his harbour-works". This can hardly be correct. The use of the ship is hard to understand anyway. What use would it have had, if it was sunk to the seafloor? Wouldn't it be pulverized by the blocks that were sunk later? What use would it have had, if it was part of the top of the island? Again, it is better to think of the symbolical deed as suggested by Boyce.
The use of stone for the lighthouse itself is suggested by lines on several depictions (nrs. 1, 7, 9, 21, 22). This could be tufa, travertine, or marble revetment. Marble revetment is reported by Flavio Biondo in the mid-fifteenth century. Other materials may have been used in the interior. On the Torlonia-relief (nr. 14b) opus reticulatum seems visible.
Openings in the tower
The ancient depictions show four kinds of openings in the tower: large, arched openings; rectangular doors; rectangular or square windows; short and long vertical lines. The latter are most likely high and narrow windows ("slit windows"). The long lines may be regarded as a representation of several of these windows. For the interpretation of these openings it is important to realize, that the ancient depictions most likely show different sides of the tower.
Openings in the tower - large, arched openings
A main characteristic of the tower is a vertical row of large, arched openings in the centre of the storeys (nrs. 4, 7, 9, 12 and 23.6). On one mosaic (nr. 4) the opening on the first floor is flanked by slit windows. This combination is not seen on any other depiction and may well be an error. Another mosaic (nr. 7) shows an arched opening in the cylinder, doubtlessly an error. A further mosaic (nr. 9) shows the lower three openings with a black interior and the upper two with a white one. Was this done by the artist to break the monotony, or was there really a difference? In this same mosaic there is a black rectangle below the lowest opening, which may be an indication that there was a staircase. On the Torlonia-relief (14b) an opening may have been moved to the side, because most of the tower is covered by a ship.
It is questionable whether these openings had a real function. They are reminiscent of triumphal arches. I propose that this was a monumental facade, turned towards the sea, sending a visual message to those who came to Rome.
On other depictions there is a single large, arched opening on the first floor, with doors, windows and slit-windows on either side and on the upper storeys. This suggests that large, arched openings were present in one or more of the other sides as well. The first storey may even have been a variation of the quadrifrons-arch.
Openings in the tower - slit windows
The slit windows are as a rule in an eccentric position. On one mosaic (nr. 10) they are also in a central position, but that is presumably a decorative extension of a motif. Many modern examples of lighthouses show that there is a natural relation between this type of window and spiral staircases (of which we have an example in Ostia, in the Round Temple). These windows seem to have been another major characteristic of the tower. They may well have been in the two sides of the tower (defining the side with the large, arched openings as the front).
Openings in the tower - doors and windows
Most interesting are the two eccentric doors on the second storey of mosaic 3. Eccentric doors can also be seen on the Torlonia relief, on the third and fourth storey (14b). These doors may well have led to spiral staircases. We should then imagine that the staircase was left at the top through a hatch that gave access to the "roof" of a storey. I suggest that on mosaic 3 we see the side of the lighthouse that was facing the harbour basin. On the opposite side the spiral staircases may have been reached through the arched openings on the various levels.
Unfortunately we have only a few depictions of windows. On mosaic 3 we see two eccentric windows on the third storey. These are hard to understand. Perhaps doors are intended, identical to those on the second storey. Mosaic 1 shows doors or windows in the centre of the storeys, apparently flanked by slit windows. The white lines on all four sides of the rectangular openings may suggest windows rather than doors, and on this mosaic we may well see the northern or southern side of the tower, i.e. one of the two sides with slit windows mentioned above.
On many depictions flames can be seen that reach far out of the cylinder. The fire guided ships during the night. Pliny the Elder, discussing the lighthouses of Alexandria, Ostia and Ravenna, explains that "the danger lies in the uninterrupted burning of the beacon, in case it should be mistaken for a star, the appearance of the fire from a distance being similar" (periculum in continuatione ignium, ne sidus existimeretur, quoniam e longinquo similis flammarum aspectus est; NH XXXVI,xviii,83).
The interior of the cylinder must have been made of fireproof material. The tufa blocks of which the ovens of the bakeries in Ostia were made could have been used. On two depictions something can be seen on the exterior of the cylinder (nrs. 2 and 5): two white dots, and two white dots in a rectangle. It is not clear what is meant.
The design of the tower and the transport of fuel
The ancient depictions suggest that the lighthouse was quite wide and had many storeys, in contrast to the lighthouse in Alexandria, which had only a few storeys and was relatively slender. As a matter of fact, overviewing the evidence, graffito 18 must be a depiction of the original Pharos. Each upper storey of the lighthouse in Portus seems to have been considerably narrower than the storey below. This is a very unusual shape for a tower, and I do not know any parallels. The building looks more like a stepped pyramid than like a tower. It should be noted that it is most unlikely that the first storey carried the weight of all the other stories. We are looking at many towers, wrapped around each other.
Why did Claudius choose this design? Possibly he wanted his tower to be much different than the original Pharos, emphasizing aemulatio and not just imitatio. It is also possible that he wanted to make the tower sturdier, able to withstand storms, tsunamis and earthquakes. Yet another possiblity is, that this design made the transport of fuel to the top easier.
There are reports that fuel was taken to the top of the Pharos in Alexandria by donkeys drawing carts. This must be fiction, not fact. I fail to see how the animals would have descended safely, without stumbling, falling and stampeeding. The obvious approach would be to use ropes, pulleys and counter-weights. However, using ropes more than 100 metres long is not practical. The design of the lighthouse in Portus would facilitate the hoisting of the fuel in stages. We can only guess how this was realized in detail.