Precise dating for Constantine II's movements as emperor is virtually impossible. What we have has been analysed by Tim Barnes in "Imperial Chronology, A. D. 337-350," Phoenix 34 (1980), pp 160-166. To give some idea, this is all we have for certain:
c September 337 In Pannonia
?338 German campaign
8 January 339 At Trier
Spring 340 Invades territory of Constans and is killed near Aquileia
The sources for those are: Julian, Or 1.19a; ILS 724; Theodosian Code 12.1.27 and Chron Min 1.236.
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