ante diem xiii kalendas quinctilias

240 B.C. -- Eratosthenes calculates the circumference of the earth (I have no idea what the source for this is)

rites at the Temple of Minerva on the Aventine

ca. 165 (?) -- martyrdom of Protase

325 A.D. -- Hosius announces the Nicene Creed during the First Council of Nicaea