Later that year, Emperor Wu, at great expense, carried out the ancient ceremony of the Feng and Shan sacrifices fengshan (封禅) at Mount Tai; this involved the worship of heaven and earth and presumably a secret petition to the gods of heaven and earth to seek immortality. He then decreed that he would return to Mount Tai every five years to repeat the ceremony, but only did so once in 98 BC. Many palaces were built for him and the princes to accommodate the anticipated cycles of the ceremony.