Complex sentence: This leaves the decennalia of Theodosius I, on January 19 388, which was celebrated when the emperor resided at Thessaloniki (he remained there from September 387 to April 388).
Split into simpler sentences: This leaves the decennalia of Theodosius I, on January 19 388. It was celebrated when the emperor resided at Thessaloniki (he remained there from September 387 to April 388).