The Altar is necessary to perform miracles. As worshippers use the Altar, mana is produced and stored. Additionally, the player may sacrifice people at the Altar by dropping them in the pyre at the top of the Altar, which will instantly produce mana, as well as shift his/her alignment towards evil and gives you 2.000 mana. Each miracle has a mana cost.
There are six miracles that, once obtained, can be produced from the Altar
The expansion Black and White 2: Battle of the Gods introduces an additional four miracles.
Building an Altar has no effect on alignment.
Your population worships you here. Their devotion increases your power and magnificence.