Thieves have stolen 21 ancient skulls which are thought to be around 700 years old from a church crypt display.
The collection, which is believed to be the largest of its kind in Britain, was taken from St Leonard's Church in Hythe, Kent.
The Reverend Andrew Sweeney, from St Leonard's, said it was a "shocking and unsettling" crime.
He said: "Each skull represents the mortal remains of a human being who deserves to rest in peace."
The display in the crypt is normally open to visitors, the Diocese of Canterbury said.
The church has the "largest and best-preserved collection of ancient human skulls and bones in Britain", it added.
The skulls were thought to have been taken between 16:00 BST on Sunday and 11:00 on Monday , when a lock on a church door was found damaged.
Insp Maxine Harris, of Kent Police, said the skulls were "not free for the taking".
She added: "They are part of an important collection. We are keen to see them back in their rightful place in the crypt."