The public business of Rome, both judicial and commercial, was largely transacted in the _basilicas_, large buildings consisting usually of a wide and lofty central nave flanked by lower side-aisles, and terminating at one or both ends in an apse or semicircular recess called the _tribune_, in which were the seats for the magistrates. The side-aisles were separated from the nave by columns supporting a clearstory wall, pierced by windows above the roofs of the side-aisles. In some cases the latter were two stories high, with galleries; in others the central space was open to the sky, as at Pompeii, suggesting the derivation of the basilica from the open square surrounded by colonnades, or from the forum itself, with which we find it usually associated. The most important basilicas in Rome were the +Sempronian+, the +Æmilian+ (about 54 B.C.), the +Julian+ in the Forum Magnum (51 B.C.), and the +Ulpian+ in the Forum of Trajan (113 A.D.). The last two were probably open basilicas, only the side-aisles being roofed. The Ulpian (Fig. 57) was the most magnificent of all, and in conjunction with the Forum of Trajan formed one of the most imposing of those monumental aggregations of columnar architecture which contributed so largely to the splendor of the Roman capital. These monuments frequently suffered from the burning of their wooden roofs. It was Constantine who completed the first vaulted and fireproof basilica, begun by his predecessor and rival, Maxentius, on the site of the former Temple of Peace (Figs. 58, 59). Its design reproduced on a grand scale the plan of the tepidarium-halls of the thermæ, the side-recesses of which were converted into a continuous side-aisle by piercing arches through the buttress-walls that separated them. Above the imposing vaults of these recesses and under the cross-vaults of the nave were windows admitting abundant light. A _narthex_, or porch, preceded the hall at one end; there were also a side entrance from the Via Sacra, and an apse or tribune for the magistrates opposite each of these entrances. The dimensions of the main hall (325 × 85 feet), the height of its vault (117 feet), and the splendor of its columns and incrustations excited universal admiration, and exercised a powerful influence on later architecture. [Illustration: FIG. 59.--BASILICA OF CONSTANTINE. RUINS.] [Illustration: FIG. 60.--THERMÆ OF CARACALLA. PLAN OF CENTRAL BLOCK. A, _Caldarium, or Hot Bath_; B, _Intermediate Chamber_; C, _Tepidarium, or Warm Bath_; D, _Frigidarium, or Cold Bath_; E, _Peristyles_; a, _Gymnastic Rooms_; b, _Dressing Rooms_; c, _Cooling Rooms_; d, _Small Courts_; e, _Entrances_; v, _Vestibules_.]