Complex sentence: According to legend, the Mexicas' principal god, Huitzilopochtli indicated the site where they were to build their home by presenting an eagle perched on a nopal cactus with a snake in its beak.
Split into simpler sentences: According to legend, the Mexicas' principal god, Huitzilopochtli indicated the site where they were to build their home. The god presented an eagle perched on a nopal cactus with a snake in its beak.