Naumachia Augusti

Location

The Naumachia of Augustus was located on the right bank of the Tiber, in the area known in antiquity as Transtiberim, corresponding to part of modern Trastevere, specifically the plain now occupied by the San Cosimato Monastery. The Residents of Rome list two naumachiae in Region XIV, which encompassed Transtiberim and the Vatican area. One of these is generally identified as the Naumachia Traiani, situated in the Vatican plain. The identity of the second remains uncertain; it could refer to the Naumachia of Augustus, that of Domitian, or that of Philip the Arab. The Naumachia of Domitian has not been definitively located. It may have been dismantled during the reign of Trajan, while the existence of a naumachia under Philip the Arab is considered unlikely. Given the limited remains surviving into the 4th century, the Naumachia of Augustus is regarded as the most probable candidate for the second structure listed in the catalogues.

History

In 2 BCE, Emperor Augustus commissioned the construction of a large basin, or naumachia, on the right bank of the Tiber in an area known as the "Grove of the Caesars." The site was excavated specifically to host staged naval spectacles. That same year, Augustus organized a reenactment of a naval battle representing a conflict between Persians and Athenians. The event featured more than thirty ramming ships, including triremes and biremes, along with numerous smaller vessels. Approximately 3,000 combatants participated, likely corresponding to the crews of around thirty ships, excluding the rowers and operators of the smaller boats.

During the reign of Tiberius (14–37 CE), a naumachia was completed, featuring a large tree trunk placed on a bridge connecting the seating stands to an artificial island in the basin.

In 59 CE, Nero held festivities on boats in Augustus's naumachia. At midnight, the emperor's ship departed via a canal, likely the Naumachia's drainage channel, connecting to the Tiber River.

In 80 CE, Titus staged a naval battle in the same basin, termed the "old naumachia" (veteri naumachia), near the "Grove of Gaius and Lucius," previously known as the "Grove of the Caesars." The basin's edge facing the statues of Gaius and Lucius Caesar was reinforced with planks and platforms, enabling gladiatorial combats and a beast hunt involving 5,000 animals on the first day. The second day featured horse races, and the third day included a naval battle followed by an infantry battle with 3,000 combatants, reenacting the Athenian conquest of Syracuse. The final act occurred on the artificial island, where foot soldiers attacked and captured a wall representing the city. …

Description

According to Augustus's Res Gestae, the naumachia was constructed on a cleared area measuring 1,800 × 1,200 Roman feet (approximately 533 × 355 meters). Its design was likely influenced by Agrippa's Stagnum in the Campus Martius, which was supplied by the Aqua Virgo aqueduct and measured about 180 × 220 meters. The naumachia's average depth was estimated at 1.5 to 1.7 meters, suitable for maneuvering triremes and biremes, though possibly shallower if smaller vessels or adapted barges were used. The basin likely had a variable depth with a gentle slope toward the drainage point. It is estimated to have required approximately 250,000 cubic meters of water to operate.

The basin of Augustus's naumachia is often depicted as elliptical, possibly to minimize the water volume required. Alternatively, a rectangular plan is suggested, as curved walls better resist water pressure only in freestanding structures. Ancient sources indicate that Augustus had the area excavated, consistent with the use of sunken straight walls. Compared to the rectangular Naumachia Traiani, the basin likely had slightly rounded corners.

The Forma Urbis, a marble plan from the Severan era, shows no clear traces of Augustus's naumachia, suggesting that by this time, the site had been redeveloped to accommodate neighborhood expansion. Cassius Dio notes that the naumachia was still partially recognizable between 200 and 240 CE, likely referring to remnants around the monument's periphery, possibly depicted as parallel lines on fragment 471 of the marble plan, representing the remaining stands. In the Transtiberim area, building orientations on the Forma Urbis vary. Streets near the Tiber align with the Via Portuensis, a major road since the Republic, while further inland, they shift to a southwest–northeast axis. This change may reflect the influence of the repurposed naumachia, with new constructions aligning with its original orientation. …