The Arcane Tower is a magical defensive tower with the Reveal and Feedback abilities. Attacks land and air units.
Although the Arcane Tower is considered a human structure, other races can build one by buying an Ivory Tower from an allied human's Arcane Vault and upgrading it, since there are no other requirements.
It appears to be a fairly weak defensive tower due to its poor damage - this is true against plain units, but not against Heroes and summoned units. The Arcane Tower comes with the Feedback ability, which combusts 24 mana for every strike against a unit with mana, and deals damage equal to the mana it destroys. Against summoned units, it deals an additional 20 damage on them. This makes it excellent against discouraging hero rushes, as the tower quickly drains the enemy heroes of vital mana needed to continually harass a base.
Once the Magic Sentry technology is researched, Arcane Towers can start revealing areas of the map. Though slower than Reveal from the Goblin Laboratory and definitely weaker than the Far Seer's True Sight, it allows human players a chance to observe the map without much cost.
Arcane Towers have Heavy armor so magic units will destroy them with ease.