From The Heroes of Might and Magic III wiki

Mausoleum

The Mausoleum is the level five dwelling of the Necropolis town. It produces Liches at a rate of 3 a week.

Requires: Mage Guild Level 1, Fort, Cursed Temple, Graveyard

Cost: 2000 Gold, 10 Sulfur and 10 Ore

Upgraded Mausoleum

The upgraded Mausoleum allows the production of Power Liches.

Requires: Mage Guild Level 1, Fort, Cursed Temple, Graveyard and Mausoleum

Cost: 2000 Gold, 5 Ore, and 5 Sulfur