To the south of the palaestra of the Terme del Foro is an interesting building, that deserves more attention than it has received so far. It was probably built during the reign of Marcus Aurelius (161-180 AD).
The facade was decorated with marble. In the east part of the building we find, going from east to west: a shop, covered by two cross vaults, with a back room; a corridor, covered by a barrel vault; two staircases, accessible from the palaestra and from an open space to the south (later blocked). In the northern half of the west part of the building are four rooms that look like shops. The westernmost room was taken over from the building to the west (I,XII,9). A wall belonging to the original room is partly preserved in the north-west corner. It was concealed by a wall set against its north side.
The area behind the four "shops" was divided in three sections by piers in the north and south wall. Various doors and windows in the outer walls were blocked, possibly in the middle of the fourth century or a bit earlier. In the east part of the southern half a passage was marked by two twisted columns. In the west part are two more columns, resting on a few steps that lead to the slightly elevated westernmost room (mentioned above). These three sections behind the "shops" had geometric black-and-white mosaics with three different patterns, belonging to the early third century. In the westernmost section remains of marble wall decoration have been preserved, and here the mosaic was replaced by polychrome opus sectile, probably in the fourth century.
It has been suggested that the building as we see it now was the seat of a guild. This hypothesis was rightly criticized by Hermansen: the building is "lacking many facilities that are characteristic of a guild". Hermansen prefers to think of a lecture hall or library, buildings that could be connected with the public baths. A clue might be offered by a black-and-white floor mosaic in what we may call the vestibule of the building: the room to the west of the northernmost staircase. In a black frame a centaur (half man, half horse, with four legs) is depicted, holding a bow. There can be little doubt that this is the ninth sign of the Zodiac, Sagittarius, even though the centaur is not bearded and does not have an animal skin, which is more common. The mosaic may be from the early third century.
Becatti, who has published the mosaic, does not draw any conclusions from it. However, the location - in a vestibule - suggests that it had a clear meaning for those who visited the building. Such a meaning is not found easily in ancient sources. It may be noted however that a connection was made in antiquity between the (normally bearded) centaur Chiron and the centaur-Sagittarius. Chiron was believed to be a righteous and wise centaur, a teacher, but also a healer. This view may even have led to the modern astrological belief that Sagittarius is the sign of science, philosophy and religion, ruling the House of Philosophy. All this can be reconciled with Hermansen's suggestion. The building may indeed have been a lecture hall, or - appropriate in baths - a school of medicine.
Plan of the Sede. After SO I.