CIRCUS GAI ET NERONIS:
built by Caligula as a private course for chariot racing in the HORTI AGRIPPINAE (q.v.). It was called circus Gai et Neronis (Plin. NH xxxvi. 74) and circus Vaticanus (ib. xvi. 200), and was a favourite place for the sports and orgies of Claudius and Nero (cf. Suet. Claud. 21; Tac. Ann. xiv. 14 (?); Suet. Nero 53 (?)). On the spina Caligula erected an obelisk (OBELISCUS VATICANUS (q.v.) ) from Heliopolis (Plin. NH xvi. 201; xxxvi. 74; CIL vi. 882 =3 1911).In the fourth century the north side of the circus was destroyed to make room for the first basilica of St. Peter, and the south wall and the two southernmost rows of columns of the church were built on the three parallel north walls of the circus (see plan in Lanciani, Pagan and Christian Rome 129). In the fifth century two mausolea were erected on part of the spina, one of them being the tomb of the wife of the Emperor Honorius (see Lanciani, op. cit. 198-205; Mel. 1902,388). One of these was destroyed about 1520 (see SEPULCRUM MARIAE), but the other stood until the eighteenth century (DuP 38; Cerrati, cit.). For the mediaeval name Palatium Neronianum, see HCh 259 (S. Gregorii de Palatio). Some remains of the circus were visible in the fifteenth and sixteenth centuries, and in the seventeenth, when the new church of St. Peter was being built, the ruins were described by G. Grimaldi, whose notes are extant in several MS. copies (see Hulsen, Il Circo di Nerone al Vaticano, in Miscellanea Ceriani, Milan 1910, 256-278, and also Tiberii Alpharani De Basilicae Vaticanae Structura, published by M. Cerrati, Studi e Testi fasc. 26 (1914) xxxiv.- xxxvii.). Cerrati points out that the reason of the collapse of the old basilica was that its walls were built, not on the centre of the walls of the circus, but slightly to one side. The axis of the circus ran east and west, and the carceres were at the east end, toward the Tiber, flanked by two towers placed unsymmetrically. According to Grimaldi, the circus was 90 metres wide and 161 long, but the length is probably underestimated (HJ 657-8; LR 551-554; RE iii. 2581-2); while Cerrati determines the width as 500, not 400, palms (i.e. 111.50 metres).