After the victorious Dacian wars (in modern Romania), at the beginning of the second century AD the emperor Trajan commissioned the architect Apollodorus of Damascus to build the most magnificent Forum, the Forum of Trajan, characterized by the presence of the Column of Trajan, two libraries, the Basilica Ulpia and the square itself. The area was almost completely occupied by other Imperial Forums (the Forum of Caesar and Augustus, the Temple of Peace and the Forum of Nerva), the architect devised a ploy to get the space needed for construction of the new forum: it was cut the saddle which joined the Capitol to the Quirinale (to a height equal to that of Trajan's Column).

The space between the Forum of Trajan and the last slopes of the Quirinal was used to build the so-called "Trajan's Markets". They are an architectural complex, made by using the flexible construction technique of brick. It uses all the available space made with the cut in the Quirinal Hill and inserts environments variously arranged, on the six levels of the monument. This articulation of the environments was able to provide a gradual transition from curvilinear determined exedra of the Forum of Trajan in the straight section of the surrounding urban fabric. Trajan's Market were mostly covered by vaults, with simple barrel vaults, with semi-domes which cover the larger environments, up to complex system covering the Great Hall, with six vaults.

The presence of numerous tabernae, in particular along the external routes, is not necessarily indicative of a commercial function of the complex: even the streets flagstone which constitute the external routes are in fact mostly only accessible by stairs which exceed the differences in height and therefore chariots could not have enough space for the transportation of goods. The Markets of Trajan were intended to be a sort of "multi-purpose center," where they carried out public activities especially administrative.

The special features of this area are its constant reuse and transformation: they were the first administrative center of the Roman Forum, then noble residence, then a military fortress and a convent. Today it host the Museum of Imperial Forum, which contains fragments of their architectural and sculptural decoration and multimedia reconstructions of impact.

One last thing: when the emperor Trajan died, the urn containing his ashes (unique among emperors, under whose principality the empire reached its greatest extent) was placed inside the pomerium, right at the base of the column.