Complex sentence: After Galerius's death in 311, he was buried at Gamzigrad (Felix Romuliana) near Zajecar, Serbia; however, the structure stood empty until the Emperor Constantine I ordered it converted into a Christian church in the 4th century.
Split into simpler sentences: After Galerius's death in 311, he was buried at Gamzigrad (Felix Romuliana) near Zajecar, Serbia. The Rotunda stood empty until the Emperor Constantine I ordered it converted into a Christian church in the 4th century.