Curia Hostilia: the original senate house of Rome standing on the north side of the Comitium on axis with it, so the steps of the Comitium formed a stair of access to the curia and the Comitium was a forecourt, or vestibulum, to it (Livy 45.24.12). The construction was assigned to Tullus Hostilius (Varro Ling. 5.155), and it was regarded as very venerable, though it must have been rebuilt after the fire of the Gauls, if not more frequently. Throughout history it was, like the Comitium, an inaugurated templum (Varro ap. A. Gellium 14.7.7).

On the exterior of its west wall was displayed the Tabula Valeria (q.v.), a painting showing the victory of M' . Valerius Messalla over Hiero and the Carthaginians in 263 B.C. (Pliny HN 35.22); according to Pliny this was the first such picture in Rome. This was later incorporated in the Basilica Porcia, in which the builders either used this wall as a party wall in its construction or transferred the picture from its original location, where the new building would have hidden it, to a new parallel wall. The latter is more likely right (cf. Basilica Porcia), but cf. Asconius in Milon. 29 (Stangl 32): Porcia Basilica quae erat ei (sc. curiae) iuncta ambusta est.

Sulla restored and enlarged the curia in 80 B.C., at which time the statues of Pythagoras and Alcibiades that had stood at the corners (cornua) of the Comitium were removed (Pliny HN 34.26). In 52 B.C. the mob of his henchmen and supporters built Clodius's pyre of the furniture of the curia, and in the conflagration it and the Basilica Porcia burned (Cicero Milon. 90; Asconius in Milon. 29 [Stangl 32]; Cass. Dio 40.49.2-3). It was then rebuilt by Sulla's son Faustus and again enlarged (Cicero Fin. 5.2). For reasons that are not entirely clear, the new curia met with little favor, and in 44 B.C. it was decided to rebuild it (Cass. Dio 44.5.2). Dio's explanation that the senate wished to erase the name of Sulla from the curia seems improbable. The other explanation put forward, that a temple of Felicitas (see Felicitas [2]) was to be built on the site of the old curia, which Lepidus eventually built, is almost equally perplexing, all trace of any such temple having completely disappeared, as well as all notice apart from Dio's casual remark. The rebuilding of the curia was eventually carried out by Augustus, the Curia Iulia.

The indications are that the Comitium was oriented to the cardinal points of the compass; the line of the façade of the Carcer seems to confirm this. Until the First Punic War, at midday the accensus consulis, standing in the curia, looked south between a rostra and a graecostasis and announced noon when he saw the sun there (Pliny HN 7.212). What the landmarks were and where they lay are matters of some dispute; at so early a period they might have been quite different from their later equivalents.