Begun by Caesar to replace the old Curia Hostilia and called the Curia Julia in his honor, the new Senate House was completed by Octavius in 29 BC (who, two years later, would be given the title of Augustus). Restored by Domitian in AD 94 and reconstructed by Diocletian after the fire of AD 283, the present building was converted to a church in AD 630, which accounts for the state of preservation. In the mid seventeenth century, the bronze doors were removed to serve as the portals of the basilica of San Giovanni in Laterano (St. John Lateran). Following the prescription of Vitruvius, the height of the Curia is half the sum of its length and breadth, the ratio which he deemed correct for proper acoustics.

Although the walls now are bare, the marble floor is a beautiful example of opus sectile, in which pieces of colored stone are fitted together in figured patterns or geometric shapes. Here, porphyry rosettes alternate with pairs of cornucopias. On either side are three broad steps, which could accommodate about three hundred senators, with two low steps at the far end to serve as a dais for the presiding magistrate.

Just visible on the steps to the sides are two large marble reliefs (anaglyphs) or parapets (plutei) which were found in the Forum and may have decorated the Rostra as a balustrade. They are carved on both sides; on the back, a sow, ram, and bull being led to sacrifice (suovetaurilia); on the front, a composite scene of imperial benefaction. One depicts the possible commemoration of Trajan's alimentary program of food relief for poor children; the other, the burning of records from the Tabularium in a cancellation of tax debt, probably by Hadrian in AD 118, who remitted nine hundred million sesterces owed the State. In the background of both are several buildings: the Temples of Divine Julius and Castor; the Arch of Augustus; the Basilica Julia; the Temples of Saturn, Vespasian, and Concord; and the Rostra, itself.