Dionysius is a lunar impact crater that lies on the western edge of the Mare Tranquillitatis. To the southeast is the crater pair of Ritter and Sabine. Just to the northwest is the system of rilles designated Rimae Ritter.
Dionysius was a Greek of the 3rd century BCE, who was sent as ambassador to the court of the Indian emperor Ashoka, by Ptolemy Philadelphus."The shape of ancient thought", p367