Scored criss-crossed lines or grids are commonly found in churches and early houses.

These marks are often quite irregular and are believed to have had an apotropaic function, perhaps being seen as a trap or barrier. Common locations appear to be door and window openings and on doors themselves. Examples have been found in houses where the marks are on the back of the door to, for example, a dark roof space, presumably with the intention of stopping any malign forces passing from the roof into the house.

The motifs known as ‘merels’ derived their name from the similarity of the designs to a number of medieval board games, most notably Merels and Nine-Mans-Morris, and has led to them being thought of as smaller versions of the same games.

Gaming ‘boards’ are indeed found in churches and cathedrals, where they are located on horizontal surfaces (the games were played using counters) such as benches and window reveals. Most of the inscriptions found, however, are on vertical surfaces, where they could not have functioned in this way, so must have had another purpose or meaning.

The motifs also appear in manuscript illustrations, where they are associated with astrology and the making of horoscopes. The fact that they share many features with other recognised symbols of protection, and are found in close proximity to such symbols, suggests that they were regarded as having a similar function.

The Solomon’s Knot, or Swastika Pelta is an ancient symbol, and is commonly seen in Roman mosaics.

The motif is found in formal medieval church decoration. As a graffito it appears to be rare, although there is a particular concentration in part of East Anglia.

Its apotropaic function is based on the endless knot or line principal, by which a demon would be become fascinated by the line and follow it, thereby becoming trapped within the device.

During the middle ages it is clear that the pentangle was regarded as a powerful Christian symbol and associated with protection. According to the 14th century poem, Gawain and the Green Knight, the pentangle would inspire and protect the knight if painted on his shield, its five points symbolising the five wounds of Christ, the five virtues of knighthood etc.

Since the Reformation the symbol has become associated with the magical arts and, in more recent centuries, it has become particularly associated with Wiccan practises and Victorian concepts of ‘black’ magic.

As a graffito the pentangle appears in sufficient quantities in diverse locations for it to be regarded as an apotropaic marking. A number of Devon examples have been found to date.

Compass-drawn motifs are very common finds as graffiti and range in size from tiny – less than 2cm across, to nearly 1m (Norfolk). It has often been assumed that these designs were created by the stonemasons who built the church, either in teaching their apprentices the basics of geometry, or for other technical purposes.

It is now thought likely though that only a few were the work of masons, including the more complex and skilfully executed examples, and that the vast majority were created by other people, as ritual protection marks.

Although we use the term ‘compass-drawn’, actual compasses are rare finds in the archaeological record and their ownership is likely to have been restricted to craftsmen who used them in their work. It is uncertain what tools (quite possibly a variety) were used by other people for making these marks, but they may have included the more commonly carried shears or knives.

Among the many Devon examples, it is interesting that quite a few are imperfect circles, where the tool has perhaps slipped and the end of the line does not meet the starting point. There are also a number of rather irregular hand drawn hexafoils.