Not sure if this is common knowledge, but I haven't seen it referenced before, and it seems like it's a bit of a bug, or at least not intended. Rome has several of the best "civ builder" bonuses in the game, and some may overlook the power of the legion, which is the unit with the highest combat strength in the game at that point (str 40.) They also have this weird ability to build a Roman fort, which I found underwhelming. However, it seems that by giving legions the ability to make the fort, there must be some "builder coding" attached to that unit. The point is.... Since the devs gave the Legion the ability to make a Roman fort, they also have the ability to repair tile improvements I(and I imagine they can remove improvements as well, though I haven't tested it.) Since repairing tile improvements cost no builder charge, a Legion can repair an infinite number of tiles. This leads to an interesting strategic option for Rome, attacking a city, pillaging every tile that has an improvement and collecting tons of extra gold, culture faith, etc. as well as healing, taking the city and keeping it, then having the legions spend a few turns polishing the city's lands. It seems like a strategy befitting to Norway, but Rome does it better because of the legion's ability.