What legions did Trajan take to Dacia?

[Arahne]

There is a huge problem with IIII Flavia in Singidunum before the Dacian wars. In fact its traces could not be dated in Singidunum before Hadrians period.
Remains of castra legionis IIII Flaviae were not built before Hadrian. Remains of dubious earth-palisade fortification could not be connected to any millitary unit since that just 15 m of fossa were dug. Earliest epigrafic evidence is from II century without precise dating. Ptolomeys note on IIII Flavia in Singidunum is the most certain date to start from.
My sugestion is that it could be in VIminacium. Earliest tombstones (without Dis Manibus formula) in VIminacium belong to soldiers of IIII Flavia, not VII Claudia in fact???