Media playback is unsupported on your device Media caption Watch: Witches' marks in England

Members of the public are being asked to help create a record of ritual markings on buildings that were once believed to ward off evil spirits.

The "witches' marks" were often carved near entrances to buildings, including the house where Shakespeare was born and the Tower of London.

The symbols were thought to offer protection when belief in witchcraft and the supernatural was widespread.

But heritage agency Historic England says too little is known about them.

The symbols, also known as apotropaic marks, can be found on medieval houses, churches and other buildings, most commonly from around 1550 to 1750.

They took many forms, but the most common type was the "Daisy Wheel", which looked like a flower drawn with a compass in a single endless line that was supposed to confuse and entrap evil spirits.

They also sometimes included letters, such as AM for Ave Maria, M for Mary or VV, for Virgin of Virgins, scratched into walls, engraved on wooden beams and etched into plasterwork to evoke the protective power of the Virgin Mary.

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Known examples of witch markings include several found at Shakespeare's birthplace in Stratford-upon-Avon, Warwickshire, carved near the cellar door where beer was kept, and at the Tithe Barn, Bradford-on-Avon, Wiltshire, to protect crops.

Others have been found in caves, such as the Witches' Chimney at Wookey Hole, Somerset, which has numerous markings.

Image copyright PA Image caption The "witches' marks" were often carved near entrances to buildings

Image copyright LASSCO Image caption Others were found inside buildings, such as on an oak beam at the LASSCO Three Pigeons in Oxfordshire

Duncan Wilson, chief executive of Historic England, said: "Witches' marks are a physical reminder of how our ancestors saw the world.

"They really fire the imagination and can teach us about previously-held beliefs and common rituals.

"Ritual marks were cut, scratched or carved into our ancestors' homes and churches in the hope of making the world a safer, less hostile place.

"They were such a common part of everyday life that they were unremarkable and because they are easy to overlook, the recorded evidence we hold about where they appear and what form they take is thin."

Witchcraft in England

Image copyright Anne via Flickr Image caption Wookey Hole Caves near Weston-super-Mare where a large number of apotropaic marks have been found.