Deuteronomy 12:2

Ver. 2. And under every green tree— The use of sacred groves for the celebration of mysteries is of very great antiquity, and, perhaps, of all others, the most universal. At first, there were in these groves neither temples nor altars; they were simple retreats, to which there was no access for the profane, i.e. such as were not devoted to the service of the gods. Afterwards they built chapels and temples in them: in future times they became extremely frequented on holidays; and, after the celebration of the mysteries, public entertainments, accompanied with dancing, were held in them. See Tibullus, lib. 1: Elegy 11: ver. 51. They decked these groves with flowers, chaplets, garlands, and nosegays, and hung them about with donations and offerings, most lavishly, says Abbe Banier, in his Mythol. b. 3: ch. 7 on the sacred groves. See also Callimachus's Hymn to Diana, ver. 200 and Spanheim's note.