This grandiose and monumental thermal building was ordered by Settimio Severo. It was probably inaugurated in 216 a.C. under the reign of his son Marco Aurelio Antonino Bassiano, named Caracalla. This architectural complex of the late imperial days, covers a square 350 mt long area. It is housed inside an arcade with halls, exedrae (semicircular recess) and stairs. In the centre of the arcade there was the main body of the thermal building (216 mt. long, 112 mt. wide and 30 mt. high), with its three great rooms and other smaller rooms. The bath building was harmoniously decorated with precious marble, statues, mosaics and frescoes. The bath complex could hold an estimated 1600 bathers in its large rooms with hot, cold and lukewarm water.
The complex was also a meeting place and housed art galleries.