Complex sentence: In the first aspect he is worshipped to avert its potential danger to harvested wheat in the "Volcanalia" and his cult is located outside the boundaries of the original city to avoid its causing fires in the city itself.
Split into simpler sentences: In the first aspect he is worshipped to avert its potential danger to harvested wheat in the "Volcanalia". His cult is located outside the boundaries of the original city to avoid the risk of fires caused by the god in the city itself.