Gamzigrad (Serbian Cyrillic: Гамзиград, pronounced [ɡǎmziɡraːd], Latin: Felix Romuliana) is an archaeological site, spa resort and UNESCO World Heritage Site of Serbia, located south of the Danube river, near the city of Zaječar. It is the location of the ancient Roman complex of palaces and temples Felix Romuliana, built by Emperor Galerius. The main area covers 10 acres (40,000 m²).

In the vicinity of Gamzigrad lie the ruins of a huge Roman complex called Felix Romuliana, one of the most important late Roman sites in Europe. Early explorers believed the ancient ruins to have been a Roman military camp, because of their size and numerous towers. Systematic archaeological excavations conducted since 1953 revealed that the site was, in fact, an Imperial palace. It was conceived and built by one of the Tetrarchs, Emperor Galerius, the adopted son and son-in-law of the great Emperor Diocletian. Galerius started construction in 298 (after a victory over the Persians that brought him admiration and glory) to mark the place of his birth. The name Felix Romuliana was given in memory of his mother Romula, who was also a priestess of a pagan cult. The complex of temples and palaces served three main purposes - a place of worship of his mother’s divine personality, a monument to his deeds as emperor, and a luxurious villa for Galerius. Romuliana survived until it was plundered by the Huns in the mid 5th century. Later the site became a humble settlement of farmers and craftsmen, finally to be abandoned at the beginning of the 7th century with the arrival of the Slavs.