Complex sentence: Cortés first arrived at Zempoala in 1519 with 500 conquistadores who then made a long trip up into the highlands using the same routes used to haul maize to Tenochtitlan.
Split into simpler sentences: Cortés first arrived at Zempoala in 1519 with 500 conquistadores. Then made long trip up into the highlands using the same routes used to haul maize to Tenochtitlan.