Basilica Iulia: on the southwest side of the Forum Romanum between the temples of Saturn and Castor, filling this side in monumental grandeur. It was begun by Julius Caesar to replace the Basilica Sempronia of 170 B.C., probably about 54 B.C. (Cicero Att 4.16.8), paid for out of the spoils of the Gallic wars, and dedicated unfinished in 46 (Augustus RG 20; Hieron. a. Abr. 1971). It was completed by Augustus, but then soon burned and was rebuilt in enlarged form and dedicated in the names of Gaius and Lucius Caesar in A.D. 12 (Augustus RG 20; Cass. Dio. 56.27.5; Suetonius Aug. 29.4). It burned again in the fire of Carinus and was restored by Diocletian (Chron. 148) and restored again by Gabinius Vettius Probianus, praefectus urbi in AD 416, at which time he embellished it with statues (CIL 6.1156 = ILS 722, CIL 6.1658, 31883 = 9354, CIL 6.31884-87). Despite its rededication in the names of Gaius and Lucius, the original name persisted in use (see, e.g., Martial 6.38.6; Statius Silv. 1.1.29). Part of the basilica is represented on the Marble Plan (FUR pl. 21; Rodriguez pl. 13).

It occupied a space 101 m long and 49 m wide, bounded on all sides by streets, fronting on the street along the southwest side of the forum, with the Vicus Iugarius and Vicus Tuscus at its ends and an unnamed street behind. The central nave, 82 m long and 16 m wide, was surrounded by two aisles, each 7.50 m wide, over which there were galleries in a second storey. These aisles were all arcaded, the façade being of blocks of white marble, while the inner rows of arcading were of concrete faced with marble. There were eighteen pillars on the long sides, and eight on the short ones. The façade was embellished with an engaged order, Tuscan on the ground storey, and unfluted Ionic above. The floor was paved with marble, colored in the nave, and white in the aisles. Because the ground sloped down from the Vicus Iugarius to the Vicus Tuscus, a gradually increasing number of steps had to be introduced to bring visitors into the basilica; these increase from one at the west end to seven at the east. Between the top of these and the façade is a narrow walk, and three steps then lead into the northern aisle, while two more lead from the outer to the inner aisle. The outer aisle on the principal façade thus has much of the character of a separate portico.

At the back of the basilica, a row of tabernae with walls of tufa and travertine responding to the pillars of the arcading opened in toward the basilica, and stairs show that there must have been another storey of such tabernae above. How accessible the flat roof over the aisle may have been is doubtful; the report that Caligula threw coins to the people from it (Suetonius Calig. 37.1) need not mean it was in regular use. The roof over the central nave was a trussed gable raised on a clerestorey.

Little survives but the pavement and foundations of the arcading. Toward the northwest corner, some brick pillars and arches belong to the restoration of Diocletian. Some fragments of the architecture have been restored, but the travertine façade pillar now standing is modern and simply intended to show the architectural forms.

The basilica was especially accommodation for banking and similar business (CIL 6.9709 = ILS 7509, CIL 6.9711). Late in the first century after Christ it came to be used for he sessions of the centumviral court (Martial 6.38.5-6; Pliny Epist. 5.9.1; Quintilian 12.5.6). We are not informed about what other uses it may have served, but presumably the tabernae were government offices, and the use of the basilica was constant and heavy.

RendLinc, ser. 8.16 (1961): 53-60 (G. Carettoni and L. Fabbrini); BullCom 78 (1961-62): 37-54 (L. Fabrini); Nash 1.186-89; Coarelli 1985, 322-24.