ante diem iii kalendas septembres

490 B.C. -- battle of Marathon (according to some reckonings)

37 A.D. -- dedication of the Temple of Augustus (and associated rites thereafter)

n.b. it appears that some source has made it into the popular press suggesting Cleopatra committed suicide on this day; August 10 seems more likely ... [many of the links on my Cleopatra page are dead; more for the to do list]