Tower

Towers are structures that are able to defend themselves. Every Fort and Keep is fortified with multiple Towers - two at each Gate. The closer to the Core they are, the more HP they have and the more damage they deal. Towers attack enemy minions and Heroes that approach them, dealing damage with each attack. For this reason, towers are usually the priority targets when attacking Forts, and should usually be destroyed first.

Gameplay
Towers will attempt to attack any enemy within their range. Towers prioritize attacking in order Objectives, then the closest Summon, Mercenary or Minion and finally the closest Hero, if no other units are in their range. If a unit in higher priority group enters a Tower's range, the tower will instantly choose to retarget them. Otherwise, Tower keeps attacking the same target unit until it leaves its range, dies or in some other way becomes untargetable.

Towers can deal substantial damage and quickly destroy careless Heroes. When a Tower targets the player, they will be alerted by a special sound and a visual effect, and it is generally a good idea to move out of range as quickly as possible. Players are therefore generally advised to stay out of range of Towers unless they have some Minions present to soak up the its attacks. As soon as the last enemy Minion within range is destroyed, the Tower begins attacking enemy Heroes, and the player may want to retreat before this happens. Once reinforcements arrive, players can resume attacking the enemy Towers without fear of being targeted.

While Towers cannot withstand too much damage, the amount of damage they deal to attackers generally makes it unwise to attack them without Minions to soak up damage. However, if necessary, they can be rushed down by a group of Heroes. In default circumstances, players can slowly wear down Towers by attacking them for as long as their friendly Minions are able to withstand them.

Towers deal 50% less damage to summoned units.

Cheesing a tower
“Cheesing a tower” is just a simple label for the strategy in which the majority of a team runs at an enemy tower as soon as the gates go down and pushes relentlessly. The key to pulling this strategy off without dying is to know when to retreat. The best heroes to execute a level 1 push have a high damage output and a means of escape when the time comes to flee (like Greymane, Kharazim, Rehgar, Anub'arak, and E.T.C.).

Cheesing a tower is only beneficial on a handful of Battlegrounds. On Cursed Hollow, for instance, if you push bottom or top lane early you are creating more space for the Boss to wreak havoc. The same can be said for Battlefield of Eternity. The bigger the map the safer it is to tower push, unless the opposing team predicts where you will push towers, they will not be able to rotate in time to save a tower - this is why you dont see tower cheesing on small maps like Tomb of the Spider Queen.

Typically, at least at the pro level, the response is to trade and begin pushing as hard as you can yourself. You want to stay even in experience and by the time you get there they're going to have taken a front wall, and you get nothing out of it besides denying them a further advantage. One of the major reasons that trading is important is because when you start losing structures you start losing a safe path for rotations between lanes, which can throw a wrench in the plans of any composition that is heavily based on roaming and ganking. When you lose a structure, what you are really losing is the vision it provides.

Trivia

 * Towers had Ammunition until it was removed on December 12, 2017.
 * There used to be a third tower with every Fort and Keep, which was situated slightly behind and to the side of the main structure and served to help protect it when it ran out of ammo. It was removed on the same patch as Ammunition and its damage and Experience were distributed among the remaining Structures.
 * In April 2020, the A Call For Help Nexus Anomaly was introduced, which enabled Structures to better protect their friendly Heroes: If an allied Hero within the range of the tower was being attacked by an enemy Hero, A Call For Help was triggered, causing the tower to switch their focus to the Hero that damaged their ally until they left the range or died. However, in June 2020, A Call for Help received some changes and the aggro system was removed to help reward aggression in the laning phase of the game. The system was kept for Forts, Keeps, and Cores.