_______________ The Trajan’s forum was the last of the Imperial Rome forums and the biggest of its time, its construction ended in 112 A.C. You can access the main square through the Trajan’s Market, on the number 94 of the Via IV Novembre. They made the Trajan’s Market into a museum in 2007, here’s the website.
One of the things that amazed me the most in Rome is the size of the ruins: they're huge! It's incredible to have manage to preserve such large areas in a buzzing city like that. The Trajan's Forum is a bit special though, since it doesn't look like much from the street entrance. That's why discovering this vast main square you had no idea could be there is just a very impressive thing.