Complex sentence: Siegfried remained a loyal servant of the Holy Roman Emperors: at the death of Otto II in 983, he fought at the side of the widowed Empress consort and regent Theophanu against the ambitions of Lothair of France.
Split into simpler sentences: Siegfried remained a loyal servant of the Holy Roman Emperors. At the death of Otto II in 983, he fought at the side of the widowed Empress consort and regent Theophanu against the ambitions of Lothair of France.