Complex sentence: Perseus was invited by the Epirots to attack Aetolia and marched on Stratus, the strongest Aetolian city, with 10,000 infantry and 300 cavalry.
Split into simpler sentences: Perseus was invited by the Epirots to attack Aetolia and advanced on to Stratus, the strongest Aetolian city. He marched with 10,000 infantry and 300 cavalry.