Ancient Magic

Ancient Magic is the term that describes a series of spells in Final Fantasy XI. These are generally considered to be the 6 Elemental Magic Spells available to Black Mages only between the levels of 50 and 60. All of them take about 18 seconds to cast and do relatively similar amounts of damage. Tier 1 Ancient Magic is generally regarded as useless by the player base due to its hideous mp-to-damage ratio as well as its obscenely long casting time.

Additional Effects
In addition to the high damage, Ancient Magic weaken the enemy it is cast on to the weakness of that spell. Such as, casting Flare (Fire element) will weaken your enemy to water. Unfortunately this effect is all but useless as the Black Mage will either pull hate or be very close to doing so, in addition to having just spent a very large amount of their MP, and thus will be unable to take advantage of this effect.
 * See Elemental Wheel.

Ancient Magic II
A second level of Ancient Magic is available to Black Mages after they reach level 75. Each one of these costs 3 merit points in order to attain, and 4 then 5 points to upgrade to their maximum potential (notable however is that only 6 levels may be purchased within the group 2 category, sharply limiting the Black Mage's maximum potential- at most one can either buy all 6 spells at level 1, max only 2 spells to level 3, or buy 3 spells at level 2. Other combos may exist but few if any pursue them). The increase in damage is considerable; however, all of the Ancient Magic II spells actually cost less MP than their Ancient Magic I counterparts and can be cast in 10 seconds rather than closer to 20.