An example of Cataphract trample damage in Age of Empires II. Notice that the Militia at the rear still took damage.
Trample damage is a sub-type of Area of Effect damage. It differs from the latter in that it commonly does full damage on a primary target and only deals a small amount of it to adjacent opponents, whereas classic Area of Effect attacks deal homogeneous damage in a certain area.
It is a significant advantage on units possessing it as they may inflict more total damage per hit than their attack score alone would suggest, provided they are put in a position to hit multiple units. Trample damage is generally referred to as splash damage in other video games.
Age of Empires 
Edit
In Age of Empires, the following units deal trample damage:
Age of Empires II Edit
In Age of Empires II, the following units deal trample damage:
- (Elite) Cataphracts with Logistica deal 5 damage (unaffected by armor) to adjacent enemy units and buildings.
- War Elephants deal 50% of their attack value to all adjacent enemy units and buildings.
- Slavic infantry with Druzhina deals 5 damage (unaffected by armor) to adjacent enemy units and buildings.
- Capped/Siege Rams deal full damage to nearby enemy buildings. The Siege Ram has a greater radius. The Ethiopians can even further increase the Rams' trample damage radius by researching Torsion Engines.
- (Elite) Battle Elephants deal 50% of their attack value to all adjacent enemy units and buildings.
The bonuses of the first three unit classes may seem small, but in mass battles, they can make a great difference. Rams can effectively destroy multiple buildings at once, especially against walls that is particularly useful.
Age of Mythology Edit
There is no definitive definition for "trample damage" in Age of Mythology; however it is possible to make a mock up trample damage by modifying the game files and giving a unit "AreaAttack" whilst removing the SingleUse and AttackAction lines.
It is possible that trample damage may have been in the alpha and/or beta versions, but was removed because AreaAttack damage still damages other units when the "Effector" is dead.
Age of Empires III Edit
In Age of Empires III, all cavalry (except ranged light cavalry) have the option to enter Trample Mode which reduces their damage and increases the damage they receive, but gives their attacks an area of effect so that they can damage multiple units at a time. Its use in Age of Empires III is questionable but some units can effectively use it, sometimes due to outside influences such as Home City Cards or Native American/Asian upgrades.
All Elephants (excluding Siege Elephants), Brahmin Monk, the Sioux War Chief, Cuirassier, and Spahi already have an area of effect melee attack which does not slow them down or cause them to take increased damage, making trample mode for these units even less useful than for other cavalry.
