Towns are a gameplay concept in the Heroes of Might and Magic series. In towns players recruit heroes, purchase creatures. Heroes can learn spells.
In Heroes of Might and Magic: A Strategic Quest, towns were different only in graphics and creature dwellings. They didn't have any unique buildings. Towns in second installment weren't much different - they just got more common (available to all castles) buildings and some creatures' dwellings could be upgraded to improve their statistics.
The third game in the series brought lots of new properties for different town types: some had Artifact Merchants - an addition to the normal marketplace. Also, grail structures were introduced, which increased income and brought some bonuses to the player. Some special structures gave bonuses to hero who defended against siege. There were introduced two classes of heroes per town - one for Might and one for Magic. Also different towns could have different levels of mage guilds available - for example barbaric stronghold could build only three levels of mage guild, and tower could have all five levels with most powerful spells
In Heroes of Might and Magic IV, each town had associated magic school (except for Stronghold), has mage guilds of five levels with aligned school spells and extra buildings which add extra spells from other schools. Barbarian stronghold has some attack and defence boosting town structures. Also like in previous game each town has two hero classes associated with it with exception to stronghold which has only might-based hero barbarian. Completely new concept introduced in fourth instalment is introducing alternative dwellings - each town can build one of two dwellings for second, third and fourth levels and since one is built, the other one is disabled, though building other dwelling of the same level was possible through scripting of map.
Heroes of Might and Magic V largely returned to the Heroes III mechanics, but still features a number of changes. Strict building interdependencies have been downplayed, partially replaced by requiring just an overall number of buildings build so far ("town level"). Each faction retained an associated magic school, with every level of Mage Guild guaranteed to have a spell of that school — as well as the lowered overall number of spells. Finally, in campaigns, most towns have bonuses revealed in the town's description, like an increased population of certain creatures, additional income or a lowered price for a non faction-specific war machine.