The Market of Trajan was designed by the Trajan's architect, Apollodorus of Damascus, and built between 94 and 113 AD. The markets were a commercial center of about 150 shops and offices, set into the side of the Quirinal Hill and completing Trajan's Forum. The market complex was the world's first real shopping mall. There were "stip malls", i.e., rows of shops, sometimes on two levels in other parts of the Republican Forum-- on the Forum side of the Basilica Aemelia and the back side of the Basilica Julia, but this multi-level "mall" was an entirely new concept. The complex included a large semi-circular room that was apparently used as a lecture hall or as an Odeon. The semicircular motif was repeated in streets through and around the shopping area. Stores and offices spread up the hill in three "belts" and halls at the end of the hemicycles reinforced the shape of the complex.

The whole of the uphill side of the market was enclosed in a high thick wall of peperino stone which is very resistant to fire -- apparently a precaution, similar to that already taken behind the forum of Augustus and later behind that of Nerva to prevent the frequent fires in the Sabura neighborhood from spreading to and damaging buildings in the Forums.

Structural engineers will notice immediately that the walls of the various levels of shops buttress the new cliff on the forum side of the Quirinal hill. Trajan had cut back the hillside to make room for his vast new Forum. It was a natural to slip shops into the spaces between the buttresses to make commercial use of spaces in a typically practical Roman solution to a construction necessity.

The markets are the best-known example of modular Roman commercial construction in concrete. It is a complex architectural structure that had six major levels, though the pavements of a few corridors and rooms are at heights between the levels. The plan of each superposed level is not necessarily vertically congruent with the one below. The careful planning is evident in the relationships between the streets and shops, the functional locations of the stairways and ramps, and the openings that were built to bring adequate lighting and ventilation. The base of the semicircular brick complex is set into the hill, above which are tiers of terraces ascending the slope. At the upper end of the slope, a two-story market hall with a series of groined vaults was lined with shops on each side of a central promenade with a balcony level and clerestory openings above. The brick facades have brickwork arches and pediments and travertine lintels. Slots in the thresholds of the shops indicate that they had sliding/folding doors similar to some found in Pompeii.

The whole site was opened to the public in 2001, and several indoor and outdoor art exhibits have already been mounted in market spaces. Ramps and elevators have been added to make the markets accessible to the handicapped. It is also now possible to move through the markets to the medieval Milizie Tower, where a small museum has been opened. Access to the top of the Milizie Tower is not yet possible.  (The tower is visible in the first illustration on this page.)