337 May 22 death of Constantine at Ancyrona, a suburb of Nicomedia.
after Easter (3 April): Bishop Eusebius of Nicomedia baptizes Constantine.
22 May, Pentecost: Constantine dies at Nicomedia.
late summer: Hannibalianus, nephew and son-in-law of Constantine and husband of Constantina is put to death during the purges of the imperial family after the death of Constantine.
9 September: Constantine II, Constantius II, and Constans assume to title of Augustus.
Re: the Agonalia
Tom raises one of the (religious) ambiguities that may always surrounded Constantine. I have read some reference to the popular worship of Mithra (spelling? - an eastern sun cult I believe) during Constantine's time. For example, while Constantine was one of the junior emporers ruling from Trier over Gaul, Britian and Spain, the overall political crises engendered by the usurpative Maxentius in Rome brought together the retired emperors of Diocletian, Maximian (Maxentius' father) and Galarius (eastern Augustus) for a meeting near Vienna. There is some existent inscription relating to that meeting suggesting that offerings to Mithra were made. I don't think that Constantine was at that meeting, however.
My feeling is that both Constantine and Helena were very interested in Chistianity, and perhaps believers, before Constantine's vision in 312. If they were, however, they had to keep it very much to themselves. The retired emperor Maximian, who resided within Constantine's court in Trier (c. 308-311) was an ardent persecutor of the Christians while he co-reigned with Diocletian. One has to look carefully at Constantine's early political position as emperor to see that it was precarious, and professing even a tolerance of Christianity before his position became stable might well have been political, if not literal suicide.
Personally, the more I research this particular history, the more facinating it becomes. For example, check out the uncanny family relations between Constantine and Maximian, and you will realize that none of the Constantine-Helena story is easy.
Constantine "practiced" Christianity as of 312, but was not baptized until a few days before his death in 337. Constantine's remaining an unbaptized Christian for most of his life is precisely the issue that raises all the ambiguity surrounding his "faith".
18 August 1999 - epicenter
On 22 May 337, Constantine the Great died at Ancyrona, a suburb of Nicomedia.
Nicomedia is known today as Izmit, Turkey.