The first Harvest - it's not know how long Alachanhea the Goddess of Nature held a grudge against the humans. Some wise men think that the rude and reckless behavior of mankind made Nature hostile. Plants ot poison and harmless animals turned against the humans. Many were lost and died during this time but at some point Alachanhea stopped altering Nature and mankind was given some time to adapt. It was a time of great sacrifices and death.
The great Harvest - after two decades of rebuild and adaption Alachanhea came back from her absence and started to come after mankind again. She created monstrous creatures, big like houses and drove the humans into the outer regions and under ground. They got nearly wiped out.
The Purge - at some point the remaining people got beyond frantic. They practised rituals of namless cruelty, begging Death himself for mercy and protection. They tought their voices were unheard... but it was a child, the weakest of all Humans who rose from the caves. She turned poison into pure water, tamet the wildest animals and one touch of hers could drain all life from every being. Her name was Amat and it was Nature itself who challenged this unknown Deity. In the end Amat crushed Alachanhea and broke her into three parts. From her remains she formed three minor deities which were held responsible for the balance of Nature.
The Abbey of the Harbinger - the encounter with Alachanhea changed Amat. She became silent and secluded. Those who followed her and spread her words formed a close circle to Amat. They're called the Abbey of the Harbinger. They became a pillar of society, performing rituals of death, religious welfare, they take care of the dead bodies and of Amats personal flowers within the city.
Shrine to Amat - Each family has its own shrine of Amat. When someone dies the remains go with the family to the Herbatorium of decay. There the Sisters of Decay seperate the bones from the flesh and after a ceremony the family becomes a small shrine, carved of bones as a reminder to their faith of Amat.