The Basilica Julia was dedicated by Julius Caesar in 46 BCE – the same year that his nearby Forum was completed. Caesar funded the construction with monies taken during his highly successful campaigns in Gaul.
But his was not the first Basilica on this site. Over one hundred years earlier Tiberius Sempronius Graccus had bought a house from his father-in-law as well as adjacent butchers shops, tore them down and built in their place the Basilica Sempronia. This original building was smaller, covering roughly two-thirds of the site and positioned at the south east end (towards to the temple of Castor and Pollux).
Competing with his rival Pompey’s major Theater construction in the Fields of Mars, Caesar repaired and extended the Basilica Sempronia at the same time that he was building out the nearby Forum to the north that also bears his name.
In 7 BCE, fire ravaged the buildings around the forum with the Basilica Julia and the Temple of Castor and Pollux being particularly badly damaged. The temple was rebuilt first and rededicated in the year 6, however it took a total of 19 years for the Basilica to be repaired. When completed, emperor Augustus dedicated the building his deceased grandchildren Gaius and Lucius however this new name didn’t find common use.
The Basilica consisted of a central nave and four aisles divided by square pilasters of travertine. These were all once veneered with marble. The fronts and sides of the building were solid marble with Doric half columns projecting out of square pilasters.