Deus, qui beatum Ambrosium episcopum
catholicae fidei doctorem
et apostolicae fortitudinis exemplum effecisti,
excita in Ecclesia tua viros secundum cor tuum,
qui eam fortiter et sapienter gubernent.
Fortitudo means, in a physical sense, "strength", but is rather rare in that sense in ancient Latin. In the moral sense it is "firmness, manliness; fortitude, bravery, courage, intrepidity". Fortis the adjective also goes beyond mere physical strength.
O God, who made blessed bishop Ambrose
to be a teacher of Catholic Faith
and an example of apostolic fortitude,
rouse up in your Church men after Your own Heart,
that they may govern her wisely and bravely.