Complex sentence: One of the significant events of Darius's early reign was the slaying of Intaphernes, one of the seven noblemen who had deposed the previous ruler and installed Darius as the new monarch.
Split into simpler sentences: One of the significant events of Darius's early reign was the slaying of Intaphernes. Intaphernes was one of the seven noblemen who had deposed the previous ruler and installed Darius as the new monarch.