Demise
In 170 AD, the Temple of Demeter was sacked by the Sarmatians but was rebuilt by Marcus Aurelius. Aurelius was then allowed to become the only lay person ever to enter the anaktoron. As Christianity gained in popularity in the 4th and 5th centuries, Eleusis's prestige began to fade. Julian, the last pagan emperor of Rome, was also the last emperor to be initiated into the Eleusinian Mysteries.
The Roman emperor Theodosius I closed the sanctuaries by decree in 392 AD. The last remnants of the Mysteries were wiped out in 396 AD, when Alaric, King of the Goths, invaded accompanied by Christians "in their dark garments", bringing Arian Christianity and desecrating the old sacred sites. The closing of the Eleusinian Mysteries in the 4th century is reported by Eunapius, a historian and biographer of the Greek philosophers. Eunapius had been initiated by the last legitimate Hierophant, who had been commissioned by the emperor Julian to restore the Mysteries, which had by then fallen into decay. According to Eunapius, the very last Hierophant was a usurper, "the man from Thespiae who held the rank of Father in the mysteries of Mithras."
Read more about this topic: Eleusinian Mysteries