Airborne unit

Airborne Units, is a third type of units in Age of Mythology and Age of Empires III, after land units and Naval Vessel units. Flying units are much rarer seen, and it is by no means certain to see any in a standard game. The bonus of flying units, are that they, unlike both land and naval units, are not bound in any way by map constraints, and that they can fly over both land, sea, rocks and walls, and visit every corner of the map. Other than that, they can only be attacked by ranged units.

Airborne Units in the Age of Empires Series
In Age of Empires and Age of Empires II, the only flying units to appear, except for the Flying Dutchman Cheat Unit in Age of Empires, which was not a flying unit per se, as it could still be attacked by melee units, was the random birds that no one could control, and which existed merely for display, returning in later installments.

Age of Mythology
In Age of Mythology, the concept of flying units is most developed. There is a total of seven airborne units available in Random Map scenarios, and an additional Campaign Hero, and one Cheat Unit.

Norse: Raven (Odin only), a respawning scout unit that cannot attack, and Nidhogg, a powerful dragon, that can be summoned by Hel's God Power, available only to Loki. It is the strongest regular flying unit in the series.

Greeks: The Greeks has only the Pegasus, a scout trainable for all three Major Gods, from the Temple in the Archaic Age. The Pegasus can be obtained as a respawning unit by all Civilizations with the Relic Bridle Of Pegasus.

Egyptian: The Egyptians have the Roc, a large flying unit that cannot attack, but instead can transport units, taking them over sea, rock and enemy walls. It is trainable by Ra and Isis through worsip of Hathor. They also have the Phoenix, a battle unit that breathes fire, and can respawn from an egg if killed, trainable by Isis and Set through worship of Thoth.

Atlantean: The Atlanteans have the Caladria, a flying healer that cannot attack, available through worship of Oceanus in the Classical Age, as Gaia and Oranos, and the Stymphalian Bird, a flying bird that shoots bronze feathers at foes, available for Oranos and Gaia, through worship of Theia in the Heroic Age.

Other than that, the Hero Servant of Kronos, an extra powerful Caladria unit, appears in the campaign, but cannot be controlled by the player, if not using the scenario editor. If the WUV WOO Cheat Code is used, the player obtains the Flying Purple Hippo Cheat Unit.

Age of Empires III
Only two flying units appear in Age of Empires III, both exclusively scouts. They are the Hot Air Balloon, and the Advanced Hot Air Balloon Hot air ballons, is an ability obtained from a Home City Card in the Colonial Age for all European civilizations. It grants the Explorer the ability to set a hot air balloon anywhere on the map, where it can explore until it dies. The Advanced Hot Air Balloon is a single use unit, available with one per game, that does not die after some time. These balloons can only be killed through direct targetting of them, meaning AI players cannot take them down.