Magi and Arch Magi are level 4 creatures of Tower. They can be recruited from the Mage Tower. (Note, that the correct spelling is 'one mage' but 'many magi'.) Apprentice magi, under the mentorship of Wizards, serve as Tower troops before they become full masters of their craft. Both mage and arch mage units suffer no melee penalty for attacking adjacent enemies and reduce the casting cost of allied hero spells by two. Arch mage attacks penetrate cover and deal full damage to enemies behind siege walls.
Magi's attacks visually looks like bolts of energy, while arch magi's attacks are concentrated beams. They both use their staff to strike enemies in melee combat.
Discussion
It is not essential to upgrade magi early in the game. However, the upgraded Mage Tower only cost 5 
and 2000 
. Considering that it gives five more hit points, speed seven and no obstacle penalty, it is more than affordable. The main downside of the magi is, that Mage Tower has very steep cost.
Although the documentation says that only arch magi ignore the obstacle penalty, but at least in some versions magi this is also true for magi.
Gremlin
Master Gremlin
Stone Gargoyle
Obsidian Gargoyle
Stone Golem
Iron Golem
Mage
Arch Mage
Genie
Master Genie
Naga
Naga Queen
Giant
Titan
