Regia (Figs. 48, 73): the small building just outside the Forum Romanum between the Sacra Via and the Temple of Vesta that Numa built and either lived in (Solinus 1.21; Ovid Fast. 6.263-64, Ovid Trist. 3.1.30; Servius ad Aen. 7.153, Servius ad Aen. 8.363; Tacitus Ann. 15.41) or used as his headquarters (Cass. Dio frag. 1.6.2; Plutarch Numa 14.1). It is also said to have been the house of the pontifex maximus (Servius ad Aen. 8.363) and of the rex sacrorum (Servius ad Aen. 8.363; Cass. Dio 54.27.3; Festus 347L). However, the last is a mistake, a confusion of the rex and the rex sacrorum, for the latter's house was on the Velia and some distance away from the Regia (Festus 373L). In the historical period no one could have lived in the Regia, for it was a consecrated templum containing sacraria (Festus 346-48L; Festus 439L). The actual house of the pontifex maximus was probably the Domus Publica, connected with the Atrium Vestae, until Augustus moved the house of the pontifex maximus to the Palatine and gave the Domus Publica to the Vestal Virgins (Suetonius Iul. 46; Cass. Dio 54.27.3). During the republic the Regia was the official headquarters of the pontifex maximus. The location is assured by the existing remains.

In the Regia was a Sacrarium Martis containing an image of the god, where the ancilia and the hasta Martis were kept (Servius ad Aen. 7.603; A. Gellius 4.6.1-2; Cass. Dio 44.17.2; cf. Obsequens 6, Obsequens 44, Obsequens 44a, Obsequens 47, Obsequens 50). There was also a Sacrarium Opis Consivae, into which none but the Vestal Virgins and public priests might enter (Varro Ling. 6.21; Festus 202L, Festus 292L; Act. Arv. VIII Kal. Sept. = CIL 6.32482; Degrassi 502-3). Certain sacrifices were regularly performed there (Varro Ling. 6.12; Festus 439L; Macrobius Sat. 1.15.19 and Macrobius Sat. 1.16.30). The head of the October horse was nailed to the wall, if it had been won by the Sacravienses, and the blood of the tail was allowed to drip on the hearth (Festus 190L; Plutarch Quaest. Rom. 97). The Annales Maximi were probably kept there (A. Gellius 2.28.6), and the pontifices as a college were probably assembled there (Pliny Epist. 4.11.6).

The Regia burned in 148 B.C. (Obsequens 19; Livy Epit. Oxyrh. 50) and was immediately restored. It burned again in 36 B.C. and was restored by Cn. Domitius Calvinus, using the spoils from his conquests in Spain (Cass. Dio 48.42.1-6; Pliny HN 34.48; CIL 6.1301 = ILS 42; EE 3.265-66). Most of the architectural remains usually assigned to it in the past and much admired have now been discovered to belong to the nearby Arch of Augustus, but a number of blocks of the cornice survive in the vicinity. Tacitus (Tacitus Ann. 15.41) says that it was destroyed in the fire of Nero. It is not listed in the regionary catalogues, but it seems to be mentioned in an inscription of the late fourth century (CIL 6.511).

Deep stratigraphical excavations in 1964-1965 have revealed the history of the building. The first masonry edifice dates only to the last quarter of the seventh century; earlier there was a group of ten or a dozen huts that were deliberately destroyed to make a building plot, and their material buried in trenches. In quick succession the Regia went through five phases, often very different from one another, always in consequence of a fire, but certain elements persisted. There was always a large, irregular, but usually clearly pentagonal courtyard with a colonnade along one side, behind which opened a group of roofed spaces, fairly tightly organized. At the end of the sixth century the building received the form it was to preserve thereafter almost unchanged. There was a pentagonal courtyard with colonnades along two long sides and a group of three rooms in a block, the center one providing entrance from the street and the courtyard and giving access to a room on either side. One of these, a small trapezoid, is seen as the Sacrarium Opis Consivae, the other, preserving a large circular feature, 2.53 m in diameter, that might well be a hearth, is seen as the Sacrarium Martis. Under the courtyard is a large beehive-shaped cistern or silo for the storage of grain. There were two different decorations with architectural terracottas worked with Orientalizing friezes of animals and maenad antefixes along the eaves of the roof in the sixth-century building. After Calvinus's rebuilding, the courtyard was paved with marble.

In the Middle Ages, the seventh or eight century, the Regia was transformed into a private house. Traces of this are visible everywhere, and for its adornment architectural elements were robbed from a variety of other buildings.

Nash 2.264-67; Entretiens Hardt 13 (1967): 47-60 (F. E. Brown); PP 26 (1971): 443-60 (C. Ampolo); RendPontAcc 47 (1974-75): 15-36 (F. E. Brown); L. Bonfante and H. von Heintze, eds., In Memoriam Otto J. Brendel (Mainz 1976), 5-12 (F. E. Brown, "Of Huts and Houses"); Coarelli 1983, 56-79.