How many legions in a single battle?

[JeffF]

I wrote too soon that Antony's Army for the invasion of Parthia was the most legions gathered for a single campaign. At Philippi the Triumvirates had 19 full strength legions while Brutus & Cassius had 17 understrength legions. Counting both sides this is likely the largest number of the classic (5000 strong type) legions in a single battle. No doubt there were 3rd or 4th century battles with a greater number of the 1000 strong legions but potentially would have fielded smaller armies.

Also I misread the information about Tiberius' suppression of the Pannonian revolt. His ten legions were for a time massed into a single force comparable in size (counting auxiliaries) to Antony's.