Complex sentence: Under Latin rule, Philippopolis was the capital of the Duchy of Philippopolis, which was governed by Renier de Trit, later on by Gerard de Strem and was possibly at times a vassal of Bulgaria or Venice.
Split into simpler sentences: Under Latin rule, Philippopolis was the capital of the Duchy of Philippopolis, which was governed by Renier de Trit and later on by Gerard de Strem. The city was possibly at times a vassal of Bulgaria or Venice.