pridie nonas apriles

357 B.C. -- Aristotle observes the transit of the moon past Mars (source?)

ludi Megalesia (day 1 ... associated with the next item, obviously)

204 B.C. -- the image and cult of the Mater Magna (a.k.a. Cybele) is brought to Rome during the conflict with Hannibal on the advice of the Sybilline books

37 A.D. -- the ashes of Tiberius are placed in the Mausoleum of Augustus

186 (or 188) A.D. -- birth of the future emperor Septimius Bassianus (later known as M. Aurelius Antoninus Caesar; better known as Caracalla)