Samuel Ball Platner, A Topographical Dictionary of Ancient Rome, London: Oxford University Press, 1929.

III, Isis et Serapis. Isis et Serapis is so called because of the temples to these two Egyptian deities erected within its area. It included the Colosseum valley and the Oppius, and was bounded by Region II, the Servian wall, the clivus suburanus from the porta Esquilina west, and the prolongation of its line westward to a point north of the Colosseum, where it turned south to the Meta Sudans. This line from the porta Esquilina was the southern limit of Region IV.

Isis. A temple to which there is only one reference in ancient literature (Hist. Aug. Trig. Tyr. 25: Tetricorum domus hodieque extat in monte Caelio inter duos lucos contra Isium Metellinum pulcherrima). The third region in the Regionary Catalogue is called Isis et serapis, and on the Haterii relief (Mon. d. Inst. v. pl. 7). is an arch with the inscirption ARCUS AD ISIS (q.v.). This arch is evidently on the via Labicana. From this evidence it is clear that a temple of Isis and Serapis stood in Region III, nera the via Labicana, important enough to give its name to the region. It was also called Isium, and was built or restored by some Metellus. There is no indication of the date, but it was probably after the beginning of the empire, and perhaps as late as the second century. In the time of Constantine the name continued (Not. Reg. III). The name of this Isis appears on one inscirption that was found in the via Labicana near the baths of Trajan (CIL vi. 30915; Isidi Lydiae educatrici valvas cum Anubi et ara Mucianus Aug. lib. proc.; PT 134).

The temple was in the south-east part of the region, but its exact site is difficult to determine, for architectural and sculptural remains which may well have belonged to such a shrine have been found scattered over a considerable area of this section, from the via Labicana north to beyond the via Macchiavelli.