MACELLUM MAGNUM
the market house on the Caelian (Not. Reg. II; CIL vi. 1648, 9183) which Nero built and dedicated in 59 A.D. (Cass. Dio lxii. 18), perhaps on the site of the present church of S. Stefano Rotondo. It is represented on coins of the period (Cohen, Nero 126-130; BM. Nero 191-197, 335-337) as a circular building of two stories, with a central tholos or domed structure surrounded by colonnades. This is generally thought to have been destroyed at some later date and rebuilt at the end of the fourth century for public use, perhaps again as a market.1 It was transformed into the church of S. Stefano by Pope Simplicius (468-482); and restored with various changes by Theodore I (642-649) and Nicolas V (1453). Of the building of Nero the only remaining portions are the travertine foundations, part of the enclosure wall, and eight pilasters of the outer colonnade, but the fourth century structure was built on the original foundations and appears to have preserved in general the form of the original. It consisted of a two-storied circular colonnade, of twenty-two columns, which supported a domed roof. This was surrounded by an outer concentric colonnade of thirty-six columns, also two stories high. Outside of this was an ambulatory 10 metres wide, divided into eight segments by rows of columns (JRS 1919, 179). The alternate segments had no outer wall and therefore resembled open courts. The original circular building of Nero was enclosed by a rectangular porticus,2 containing shops, of which remains were perhaps still to be seen in the sixteenth century (Mon. d. Lin. i. 503-507 ; Mitt. 1892, 297-299; HJ 237-238; HCh 474; DAP 2. ix. 412-414; BC 1914, 358; Altm. 75-76; LR 355-359).