A Mortus' duties are twofold. First and foremost, he must make sure the power in the fortress does not run out. In order to do this, he must sacrifice live people to the Lifeweb, which will slowly drain them of blood and thus generate the much needed power. A Mortus' second duty is to bury or encrypt the bodies of the dead.
Blood for the Blood God! Edit
The Lifeweb is the fortress' power generation device. It is located behind two sealed doors in the depths of the Mortus' sanctum.