Thieves have stolen five large millstones from Jill windmill on Clayton Hill, near Hassocks.
The stones, which each weigh about half a ton, are at least 100 years old.
A police spokesman said: “Thieves visited the windmill sometime since Saturday 2 February and stole these four foot wide stones which are part of this local landmark. One is a distinctive dark grey volcanic lava stone with an inscription of oie 1721. Another is a standard millstone but with four holes drilled into it. At least four people would probably have been needed to move each stone and a hedge was cut to enable them to drive them away.
“We would appeal to anyone who saw any suspicious activity, has any information or been offered these stones to contact police on 101 or the independent charity Crimestoppers anonymously on 0800 555 111.”