Complex sentence: When the Persians and the Ionians arrived, the Naxians were prepared for a siege and they held out for four months before the Persians and their allies retreated as they had run out of gold and resources.
Split into simpler sentences: When the Persians and Ionian allies arrived, the Naxians were prepared for the ensuing siege. Naxos successfully held out for four months until the Persians and their allies retreated due to the exhaustion of gold and resources.