Ancient Aztec religion is the Mesoamerican religion of the Aztecs in the 14th and 15th centuries. It was a religion based solely around worship to their gods. Like other Mesoamerican religions, it had elements of human sacrifice in connection with a large number of religious festivals which were held according to patterns of the Aztec calendar. It had a large and ever increasing pantheon; the Aztecs would often adopt deities of other geographic regions into their own religious practice. Aztec cosmology divided the world into upper and nether worlds, each associated with a specific set of deities and astronomical objects.