Note to JULIUS CAESAR, 3.1.108, 'even to the market-place'
The conspirators must be going to the Forum, which began about 500 BCE as a market-place, and had become, by Caesar's time, the heart of Rome and the primary venue for elections, public speeches, criminal trials, social gatherings, business dealings, and religious ceremonies. The Forum was so crowded that Caesar had a new one built to the side of the original. The drawing below shows what the Forum of Caesar might have looked like on a very slow day.

Forum of Caesar