Vandals scaled scaffolding on an ancient Oxfordshire church tower before ripping stones from the parapet and lobbing them at floodlighting.
The damage, at St Mary's Church, Garsington, has disrupted a £200,000 restoration programme.
It is not known how much the vandalism will cost to repair or how badly it will set back the restoration scheme.
Vicar the Rev Richard Cowles said: "It's very sad that mindless idiots get their kicks from hurting a building that has been here more than 800 years, and that is of great meaning to lots of people in the community.
"It's a building which people are trying very hard to retain for the village.
"The vandals climbed up the scaffolding to the top of the tower, dislodged masonry from the parapet and threw heavy stones down, aiming at the floodlighting equipment.
"It was an extremely dangerous thing to do. They have used considerable force and probably kicked at the masonry, and they have damaged the windows, which aren't glass but have wooden louvres and wire netting.
"It's a very old tower, which dates from about 1190 and we're restoring the stonework inside and out.
"It's a big and expensive project and this damage means we can expect it to cost even more money, but it's impossible to put a figure on how much.
"It means we are now having to keep the church locked. Normally it would be open in the day time, but we are having to lock it because we are worried the vandals might come back and do further damage.
"There are a lot of people in the village who are supporting the project financially."
Mr Cowles said the church vandalism was the latest in a string of incidents in the village.
"There was graffiti and damage to the gates on the recreation ground recently and there have been problems around the village shops."
Thames Valley Police spokesman Victoria Bartlett said: "This was a dangerous and mindless act of criminal damage."
Anyone with information should call police on 08458 505505 or Crimestoppers on 0800 555111.
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