When the sons of Constantine massacred all their close relatives, they spared a couple of their cousins. Gallus and Julian were too young to pose any immediate threat so they didn't have to be killed straight away. But as their parents had been killed something needed to be done with them, so they were held captive. Was there a long term plan for them? It is hard to say. Given that they had an empire to run, probably their captors forgot all about them. They were safely out of the picture and there were plenty of other things going on.
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Labels: Gibbon, Julian the Apostate