The primary reason why Romans sacrificed animals and built temples was to please their gods. This was an important aspect of their religious beliefs and practices. Sacrificing animals and offering them to their gods was seen as a way to gain favor and blessings from the divine entities. Building temples was also a way to honor and worship their gods, providing a sacred space for rituals and worship ceremonies. While it is possible that some Romans may have also aimed to improve their governing skills or impress other civilizations through these religious practices and structures, the main motivation behind such actions was religious devotion.
