Visitors to St Albans Abbey absorb a huge amount of history as they wander down the longest nave in the country or visit the Shrine of Alban.

The history of the building is well documented but not so much is known abut the wall paintings on the Norman piers between the nave and the north aisle as well as on the soffits of the arches.

They are believed to be the most extensive set of medieval wall paintings surviving in the great English churches and some of them probably date back to the 12th Century.

But like wall paintings in churches across the country, their origin and purpose is something of a mystery and even the experts can only speculate about why they were painted and what purpose they served.

A new book by Roger Rosewell entitled Medieval Wall Paintings incorporates several of the fragments from St Albans Abbey among a wealth of illustrations. It examines the purpose of wall paintings, their subjects and how they were made as well as why most were whitewashed during the Reformation to save them from being destroyed.

Rosewell rejects the commonly-held belief that wall paintings acted as “books for the illiterate” who couldn’t read so had to look at paintings. He believes the explanation is much more complicated and comes down to issues such as who commissioned them and why, where they were situated in a church, the intended audience and how the images collaborated or interacted with other aspects of worship.

They were, he suggests, preceded by large-scale ornamental patterns in some churches with the masonry patterning, designed to “foster illusions of depth” in St Albans Abbey held up as a good surviving example.

Some had texts either above or below them. One such is the painted text below the wall painting of the Resurrected Christ with Doubting Thomas in the Abbey which bears the words of a devotional poem that in modern-day translation reads “I am on the cross for you”. Rosewell points out that it was part of a larger scheme which included a complementary image of the Crucifixion and two pillars in contrasting colours.

On the question of how they were created, he also pulls out an example from St Albans Abbey including a striking image of St William of York which was built up in layers of pigment and finished with a translucent glaze making it remarkably well preserved.

The wall paintings at the Abbey attract visitors throughout the year and offer a range of ecclesiastical images from the Crucifixion, the Annunciation and the Virgin and Child to Christ in Glory. Some are just fragments or outline but they must once have played a valuable part in the life of the Abbey.