Mausoleum of Maxentius, Ancient imperial mausoleum on Appian Way, Rome, Italy

The Mausoleum of Maxentius is a circular tomb on the Appian Way, of which only the semi-underground floor survives. Its outer wall, 3.5 m thick, is lined with alternating semicircular and rectangular niches, each with a small window, and surrounds a central octagonal pillar with matching niches. A 26-step staircase led to the lost upper level.

Emperor Maxentius built this family tomb between 306 and 312 AD as the burial place for his son Valerius Romulus. The structure originally rose as a two-story rotunda, but only the underground level survives in its complete form today.

The tomb's name alternates between Maxentius and his son Valerius Romulus, buried here probably in 309, perhaps the only burial. The complex sits beside several catacombs, and Roman custom required tombs outside the city walls. The 18th-century house masking the tomb from the Appian Way was a farmhouse later converted by the Torlonia family, who held it until 1943.

The semi-underground crypt lies 2.33 m below today's ground level, reached by a staircase; the upper storey is gone. An 18th-century house stands between the tomb and the Appian Way, hiding the entrance that a columnar porch once framed. The site reopened to the public in 2014 after restoration.

The crypt's walls are 3.50 m thick, lined with niches about 3.60 m deep that alternate between semicircular and rectangular shapes, each with a small window. The central pillar has matching niches, and the whole plan follows a module of eight Roman feet.