Rotunda Galerius, also known as the Rotunda of Saint George, is a majestic ancient structure located in the heart of Thessaloniki, Greece. This impressive cylindrical building with a massive dome was originally built in the late 3rd or early 4th century AD as part of the grand funerary (or, according to another version, palatial) complex of the Roman Emperor Galerius. The Rotunda was designed as a key element of an architectural ensemble that also included the Triumphal Arch of Galerius and his palace, and was connected to the arch by a gallery and a colonnaded portico.

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Over its long and eventful history, Rotunda Galerius has undergone numerous transformations reflecting the change of eras and cultures. In the early 5th century, this monumental building was converted into a Christian church dedicated to Saint George the Triumphant, which gave it its second, widely known name. From 1590, during the period of Ottoman rule, the building served as a mosque. After the liberation of Thessaloniki in 1912, the Rotunda was returned to the Christian community and later turned into a museum of Christian art, housing priceless artifacts and unique mosaics.
Today, Rotunda Galerius is one of the most significant and visited historical landmarks in Thessaloniki. In 1988, along with the Arch of Galerius and other early Christian and Byzantine monuments of the city, it was rightfully included in the prestigious UNESCO World Heritage list. It is a unique example of Roman architecture, perfectly preserved to this day, attracting tourists and researchers from all over the world with its rich history, impressive size, and monumental beauty, serving as a witness to the city's centuries-old history.