I think that any arcane units currently sitting on an Ancient Tower would temporarily acquire Perfect Sight, Sentry I, Sentry II, Channeling I, Channeling II ... this would be representative of having "activated" the Tower's defenses for your own purposes.
Maybe you have to explore the Tower at least once to activate it for your own purposes? Maybe you have to explore with a mage, and once you get a positive result, the tower changes to your Civ-color and gives an advantage to your units only. Then later another nation can explore it to do something similar. Melee units (or maybe only seige??) would be able to raze it down without trying to explore it, of course. Also, they are buildable, and if you build it, it starts with Your Civ Color. Can explore starting at KOTE, however can only Build it starting with Arcane Lore??