What did the Tiantan, Ditan, Yuetan and Ritan in Beijing do before?

In the early Ming Dynasty, the emperor offered sacrifices to the gods of heaven and earth, the sun and the moon, the stars, the rain and the wind and thunder. It was not until the ninth year of Jiajing in the Ming Dynasty (1530) that the gods were worshipped in the suburbs. Later, a ball altar was built at the southern end of the Heaven and Earth altar (now the Hall of Praying for the Year, also known as the Temple of Praying for the Valley), which became a veritable "Temple of Heaven", also known as the Temple of Heaven, and was used by the emperor to worship the heaven every winter to the sun. The Hall of Praying for the New Year in the Temple of Heaven, namely, the altar of praying for the grain (the original altar of heaven and earth), became the place where the emperor prayed for a bumper harvest on the fifteenth day of the first lunar month every year. Ditan was built outside Andingmen, where emperors of Ming and Qing Dynasties offered sacrifices to land gods from summer to Sunday every year. Outside Chaoyangmen, there is an altar to worship the sun at the vernal equinox. The moon altar built outside Fuchengmen is the festival of the autumnal equinox moon. Xiannongtan, located on the west side of Yongdingmen, is a place for offering sacrifices to Shennong. Every year, the emperor comes here on the auspicious day of spring and February to worship the thunder. Tai sui altar is located in the northeast of Xiannong altar, because Tai sui is the god of age, and the emperor needs to choose auspicious days to sacrifice here in spring and summer every year in order to be auspicious and prosperous. The first silkworm altar is located in the northeast corner of Beihai Park. In the second month of spring every year, the Queen will come here to pay tribute to Mulberry to show her concern and attention to agricultural and sideline production.