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Regio I - Forum - Circular structure (Sacello dei Lares Augusti)

Virtually in the centre of the Forum, to the south of the Decumanus Maximus, are the remains of a brick circular structure (outside diameter 4.50 m.). It may have been built during the reign of Trajan (98-117 AD), or a bit earlier. A marble cornice runs around the lower part of the outer wall. Marble slabs were probably fastened in holes in the top of the cornice. Inside are six rectangular niches. The northern one is a blocked entrance. On the floor is a white mosaic.

The structure was regarded as a basin or fountain-house (nymphaeum) until 1962, when Bloch proposed that it was a compitum. Compita were shrines at crossroads where the gods of the crossroads (Lares Compitales) were worshipped, together with the household gods of the Emperor (Lares Augusti). Bloch suggests that a number of curved inscriptions from 51 AD, found at some distance, belongs to the structure. He also states that the structure cannot be a nymphaeum, because there are no remains of hydraulic mortar, and because it is not clear how water reached and left the fountain.

His view came under attack in 1994, by the present author. Remains of hydraulic mortar (opus signinum) can be seen in the corner between the mosaic floor and the wall. One of the niches has a hole in the back, below a relieving arch (niche 3, which is directly above an old well). The bottom of this niche slopes downwards towards the floor of the structure, starting a little below the present level of the Forum. It was meant for the supply of water. Furthermore, between 1994 and 1996 German archaeologists checked whether the curved inscriptions would fit the outer wall. This was not the case (oral communication, 1996). So this is a nymphaeum, or a pool, after all ... or so it seems.

Plan of the structure

Plan of the structure
(Jan Theo Bakker).
Some reflections on the circular structure

Originally the nyphaeum must have contained four statues, one (in niche nr. 2) opposite a row of three (in niches 4-6). Niche nr. 3 was used for the supply of water, the present niche nr. 1 was an entrance. In a fountain-house we may expect statues of Nymphs, goddesses related to lakes, rivers and wells. Several inscriptions document the cult of the Nymphs in Ostia, and various representations of the sea-nymph Leukothea (appropriate in a harbour city) have been found, for example in the Caseggiato dei Triclini (I,XII,1), to the south-east of the Forum. In the nearby Caseggiato del Larario (I,IX,3) a marble well-head was found, probably re-used. It was made for some new well in 197 AD, "after an admonition by Ceres and the Nymphs". It is possible that the circular structure hosted a statue of Ceres, opposite three statues of Nymphs, and that the well and well-head were originally on the Forum, inspired by the circular structure. This idea is very speculative, but some support is found.

We must note a few curious aspects of the structure. There is more to this little edifice than meets the eye.

  • The niche with the hole causes a curious asymmetry. The normal length of wall + niche + wall is 0.65 + 0.88 + 0.65 = c. 2.20. For niche 3 the figures are 0.54 + 0.57 + 1.09 = c. 2.20. Why wasn't this 2.20 divided in the "normal" sections?
  • One would expect the single niche and the central one of the row of three niches to be on the axes of the Decumanus and Cardo (the axes also of the Castrum and Forum); but these two niches are placed diagonally toward these axes.
  • The peculiarities mentioned above made me think of a combined sundial and water-clock. But a much better suggestion may come from Raissa Calza. Discussing the foundation of the colony, she wrote about the structure: "A fountain, built later, perhaps recalls the ancient mundus of the Castrum, the sacred well at the centre of the intersection of the two as yet unpaved roads [Cardo and Decumanus], worshipped like a relic". This brings to mind the old well below the niche that supplied water to the fountain. This well may have determined the position of niche 3.

    If the position of niche 3 was fixed, we can understand the deviating measurements 0.54 + 0.57 + 1.09: these restored regularity to the structure, creating angles of 0, 45, 135 etc. degrees. But this still does not explain the diagonal axis; there could have been one statue in niche 4, opposite statues in 6, 1 and 2. The hypothetical presence of Ceres may now be significant. We know of the mundus Cereris, an entrance to the underworld (Festus; inscription from Capua mentioning a sacerdos Cerialis mundalis). The builders may have wanted Ceres to be close to niche 3, which would explain the diagonal axis. The diagonal axis may have been used as an indicator that this was not a mere decorative structure, that there was something special, out of the ordinary about it.

    Perhaps we can go even further. The main deity worshipped in Ostia was Vulcanus, and it is conceivable that there was a Volcanal on the Forum of Ostia (a simple structure, without a roof), comparable to the Volcanal on the Forum in Rome, which was near a structure that recalls or may be called a mundus: the Lacus Curtius.

    In Rome sacrifices took place each year, on August 23, to ward off fire: to Vulcanus, the Nymphs and other deities. After the fire of Rome in 64 AD measures were taken to prevent similar catastrophes, including prayers addressed to Vulcanus, Ceres and Proserpina.

    One thing is certain however. The circular structure must have been a landmark. Because it is in the centre of the Forum, many people must have gathered and rested there, as many tourists do today. Further research may indicate whether it was only a nice fountain, or whether the diagonal axis is telling us that "X marks the spot" - the religious centre of the colony.

    Hypothetical reconstruction drawing of the structure

    Hypothetical reconstruction drawing of the structure.
    From the south-west (Jan Theo Bakker).


    General view from the north-west. Photograph: Jan Theo Bakker.

    Detail of the interior, from the north-west. Photograph: Jan Theo Bakker.

    The curved inscriptions, now stored in the Piccolo Mercato. Photograph: Jan Theo Bakker.
    [jthb - for this page I would like to thank Bill Thayer - 13-May-2006]