The Portrait of the Four Tetrarchs is a porphyry sculpture group of four Roman emperors dating from around 300 AD. The sculptural group has been fixed to a corner of the façade of St Mark's Basilica in Venice, Italy since the Middle Ages. It probably formed part of the decorations of the Philadelphion in Constantinople, and was removed to Venice in 1204 or soon after.

Spolia from the Fourth Crusade, the statues were originally designed as two separate sculptures, each consisting of a pair of armoured late Roman emperors embracing one another. The paired statues stand on plinths supported by a console of the same stone, and their backs are engaged in the remains of large porphyry columns to which the statues were once attached, carved all of a piece. The columns no longer exist, and one emperor pair is missing part of the plinth and an emperor's foot, which has been found in Istanbul. One statue pair has been sliced vertically and is missing a large portion of the right-hand emperor's right side, while another vertical slice divides the two figures and has sawn through their embracing arms.