The Dacian Wars, which were fought against King Decebalus, financed the last and grandest of the imperial forums, Trajan's forum (forum Traiani). The main entrance to it was through a triumphal arch. Trajan's Forum, which may have been started under Emperor Domitian, contained the "forum proper, the basilica Ulpia, the column of Trajan, and the bibliotheca [Greek and Latin libraries], and extended from the forum Augustum north-west between the Capitoline and Quirinal hills," according to Platner. After Trajan's death, Emperor Hadrian built a temple of Trajan on the northwest side of the libraries.
The width of the area excavated to build the forum was 185m in width and 310m in length. The forum proper was 116m wide and 95m long. Half circles (referred to as Hemicycles), 45 meters deep formed two sides of it. The first floor of the semi-circular structures was probably for shops, leading some modern writers to describe the area anachronistically, but understandably, as a shopping mall. [See Roman Apartments.]