ante diem xvii kalendas maias

ludi Cereri continue (day 4)-- games in honour of the grain goddess Ceres, instituted by/before 202 B.C.
Fordicidia -- an obvious fertility ritual in which a pregnant cow would be sacrificed to the earth goddess Tellus
421 B.C. -- Peace of Nikias brings the first phase of the Peloponnesian war (a.k.a. the Archidamian War) to an end (by one reckoning)
69 A.D. -- the forces of emperor wannabe Vitellius defeat the forces of emperor wannabe Otho
251 A.D. -- Martyrdom of Maximus and Olympiades in Persia