Mortars are the player's heavy defenses. Whenever an enemy comes into range, it blasts out an explosive shell with a low frequency "ping".
Mortars have high damage per attack, deal splash damage, and shoot an explosive shell every 5 seconds. Their splash damage, combined with their long range, make them deadly weapons against large numbers of weaker enemies such as Barbarians, Archers or Goblins. Its major disadvantages are its inability to attack enemies at close range and its low rate of fire. (Tile range of "blind spot" is 4 tiles.)
Due to the fact that the Mortar's shell takes a long time to reach its target (over 1 second), fast troops like Goblins can easily dodge its attack if they are moving when the Mortar fires.
Mortars should usually be placed towards the center of your base, preferably behind at least one set of Walls. Its long range allows the Mortar to attack behind other structures. Since the Mortar deals heavy splash damage, it can quite rapidly eliminate attacking Troops; multiple Mortars ensure more destruction and damage. Take care when upgrading, as many players use this as a chance to attack. For this reason it is often a good idea to only upgrade one Mortar at a time.
At each level the Mortar can one-shot a similar-level Archer (at level 1 it can one-shot level 1 Archers, level 2 can one-shot level 2 Archers, etc.).
Putting a Mortar and Wizard Tower together makes a smart pair, because the Mortar covers a large area while the Wizard Tower helps protect the Mortar from mass air troops and covers the Mortar's blind spot.
It is a good idea to place Mortars near each other, without them being in the same cell if possible. When more than one Mortars' range overlaps, it creates a kill-zone where almost no ground troops can survive.
The Mortar's blind spot, low rate of fire, and inability to target air troops makes them vulnerable to a wide variety of different attacks. Fast melee troops such as Barbarians or Goblins (after all resource structures are destroyed) can rush to the Mortar and quickly enter its blind spot. Archers can also be effective if they are positioned in a circle around the Mortar or if protected by a meatshield .