Complex sentence: Its precipitous sides gave it an almost impregnable position and the lesser hills round it were well defended by the Germans and it was necessary for them to be mastered before Centuripe could be tackled.
Split into simpler sentences: Its precipitous sides gave it an almost impregnable position. The lesser hills round it were well defended by the Germans and it was necessary for them to be mastered before Centuripe could be tackled.