The Circus of Nero

Long before Bernini’s colonnade framed the world’s most famous piazza, a private racecourse stood on the Ager Vaticanus, low-lying ground on the Tiber‘s right bank, given over to gardens and cemeteries. The emperor Caligula laid it out in the gardens associated with his mother, Agrippina the Elder. Pliny the Elder calls it the circus Gai et Neronis, the circus of Gaius and Nero. Gaius was the birth name of the emperor better known as Caligula, who built the course. Nero is named alongside him, which has led scholars to think he enlarged or reworked it, though what he actually did there is not recorded. The structure also went by the plainer name circus Vaticanus.

The circus ran on an east-west axis, with the starting gates, the carceres, at the eastern end toward the river, flanked by two towers set slightly off from each other. At its center Caligula raised an obelisk brought from Heliopolis in Egypt, carried in a ship whose enormous timbers Pliny singled out as a wonder. That obelisk is the one constant in the site’s long history. It is the only ancient obelisk in Rome never to have fallen, and in 1586 the architect Domenico Fontana moved it, upright and intact, to the middle of Saint Peter’s Square, where it stands today.

The events that gave the circus lasting fame took place around it, in the gardens and along its edges. Roman tradition sets Nero’s punishment of Christians after the great fire of AD 64 in the Vatican gardens and their circus, and later Christian memory located the martyrdom of Saint Peter close by. A cemetery grew along the Via Cornelia on the northern flank, and it was over the grave venerated as Peter’s that Constantine built the first basilica of Saint Peter in the fourth century. Construction consumed the northern side of the circus. The builders set the church’s southern wall and its columns on the circus walls, but not squarely on top of them. That off-center footing left the old basilica structurally unsound, and it was one of the reasons the building was demolished and replaced in the sixteenth century.

Later centuries added their own layers. In the fifth century two mausolea rose on the spina, the central barrier of the track, one holding the wife of the emperor Honorius. Ruins remained visible into the Renaissance, when the antiquarian Giacomo Grimaldi recorded them as the new basilica was being built. From his notes come the reported dimensions of roughly ninety meters wide and one hundred sixty-one long, though the length is probably too short.

Modern archaeology has recovered the plan piece by piece. Excavations beneath the Vatican car park in the mid-twentieth century, led by Filippo Magi, confirmed the line of the walls and the position of the gates, while work under Saint Peter’s has traced the surrounding necropolis in detail. The result is a rare case in which a vanished Roman building can be read through the church that replaced it.

FURTHER READING

1. Townend, Gavin. “The Circus of Nero and the Vatican Excavations.” American Journal of Archaeology, vol. 62, no. 2, 1958, pp. 216–18. JSTOR, https://doi.org/10.2307/502357. Accessed 24 July 2026.
2. Humphrey, John H. Roman circuses: arenas for chariot racing. Univ of California Press, 1986.
3. Gee, Regina. “CULT AND CIRCUS ‘IN VATICANUM.’” Memoirs of the American Academy in Rome, vol. 56/57, 2011, pp. 63–83. JSTOR, http://www.jstor.org/stable/24616437. Accessed 24 July 2026.
4. Iversen, Erik. “The Date of the So-Called Inscription of Caligula on the Vatican Obelisk.” The Journal of Egyptian Archaeology, vol. 51, 1965, pp. 149–54. JSTOR, https://doi.org/10.2307/3855627. Accessed 24 July 2026.

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. 201), 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=31191).

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; Mél. 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 Hülsen, 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).