Experience and Heroes

All units in Gladius, even stationary fortifications, gather experience. Once enough experience is gathered by a unit, it will gain a new. Units start at level 1 and have a maximum level of 10. Every level above the first increases the unit's and   by 5% as well as  by 10%. Heroes also get 1 skill point per level that they can spend on one of their 4 hero abilities.

Whenever a unit is destroyed, all units up to 3 tiles away from it and allied to the killer receive experience. Every unit in the radius gets the same amount of experience, no matter how many units there are. The amount of experience a unit will give out upon death depends on its strength can be checked by selecting it and mousing over its.

This chart shows the experience needed to reach a certain level:

Heroes
Heroes are a special type of unit. Through experience they are able to learn and improve 3 special abilities as well as 1 especially powerful elite ability. Heroes can upgrade their abilities to the second tier at level 3, to the third tier at level 5 and can learn their elite ability (which cannot be upgraded) at level 6. With every live copy of a hero unit you currently control, that hero unit's recruitment cost is increased by its base cost, making it more and more expensive to have multiple copies of the same hero type. Every hero also has innate (meaning they take only half damage, not that they take less damage from heroes). Additionally, heroes have the ability to purchase and equip items from a Jokaero Trader Encampment. Every hero has for 6 items. Another way for a hero to gain a level is by purchasing and using a Forbidden Knowledge item.

Heroes built on turn 81 start out with 0.5 experience and start with an additional 0.5 experience every following turn. This chart shows from which turns on a hero unit starts out at a specific level:

If you notice that you are close to one of these turn counts, you might want to hold off on the construction of a hero unit, so that you can ensure they will receive another free level.