From The Heroes of Might and Magic III wiki

[edit] Guardhouse

The Guardhouse is the level 1 dwelling of the Castle town. It produces Pikemen at a rate of 14 a week.

Requires: Fort

Cost: 500 Gold, 10 Ore

[edit] Upgraded Guardhouse

The upgraded Guardhouse allows the production of Halberdiers

Requires: Fort

Cost: 1000 Gold, 5 Ore