Also possibly fictional, but you never know. The motto of all Roman legions as well as of Rome was the acronym SPQR, Senatus Populus Que Romanus, meaning "The Senate and the People of Rome�, i.e. �In the name of the senate and the people of Rome�.
This acronym was carried on battle standards by the Roman Legions. Each legion had a name and a symbol, but not a motto. For example the name of the �legio II� was: �Legio II Adiutrix Pia Fidelis �(helper faithful and loyal), while its symbols were a Capricorn and Pegasus. The men of that legion may well have said �faithful and loyal� to each other just before going into a battle.
As for �Strength and honour� (Latin, �Vires et Honor� or other variants) it was not the motto, or battle talk of the legions in the strict sense of the word, but certainly the ideals the Romans fought for.