Moat

Moat is a defensive structure in front of the walls in towns with Citadel or Castle. The original Restoration of Erathia version or the Armageddon's Blade did not have moats, as they were introduced in Shadow of Death expansion. The moat has different effects in siege combat. Both attcking and defending creatures:

on the moat suffer additional 10% damage from non-magic attacks
are not able to move across the moat during combat round, but are forced to stop on the moat for the the rest of the round
take damage from entering the moat and for each round they stay in this moat.

Damage:

All moats cause damage to creatures if they are forced to cross the moat. The amount of damage depends on the town type as follows:

Castle has water as moat and cause 70 points of damage
Rampart has brambles as moat and cause 70 points of damage
Stronghold has wooden spikes as moat and cause and cause 70 points of damage
Necropolis has boneyard as moat and cause 70 points of damage
Fortress has boiling tar as moat (2 hexes wide) and cause 90 points of damage
Dungeon has boiling oil as moat and cause 90 points of damage
Inferno has lava as moat and cause 90 points of damage
Tower does not have a moat per se, but has landmines in front of the wall.

Tower's Land Mines

Tower's land mines work in a similar way as the the spell of the same name. The damage it calculated with the formula:

10 × power + 50

Tower mines

The landmines are cast with advanced Fire Magic on Spell Power 10.
They are the only town defending system influenced by the visiting hero.
Protection from Fire will reduce the damage they make.
Defending creatures won't let the mines explode.

Increasing damage

They will do 150 damage at minimum. Stronger hero stats will increase the damage.

To increase the damage of the land mines the hero needs:

Spellpower 14 without/with basic Fire Magic
Spellpower 11 with advanced Fire Magic and
Spellpower 6 with expert Fire Magic

The Orb of Tempestuous Fire will always increase the damage by 50%. The hero does not need a Spell Book.

Fire immunity / Spell resistance

The mines will not explode on creatures with fire immunity.
The mines will not affect creatures with 100% spell immunity. (Some dragons.)

Removing / disabling them

The mines can be Dispelled. With expert Water Magic you can dispel all the mines at once.
If either of the heroes has the Recanter's Cloak equipped, all creatures will be immune to the mines.