The Grand Masters' crypt - the final resting place of the first Grand Masters of the Order of the Knights of St John - is undergoing restoration at St John's Co-Cathedral in Valletta.

On the initiative of the St John's Co-Cathedral Foundation, conservators from London's Courtauld Institute, which specialises in the conservation and restoration of wall paintings, are currently working within the crypt.

They are testing materials to be used to consolidate weak plaster areas and stone tombs, removing salt veils, as well as cleaning the marble and bronze tombstones.

Conservators have been carrying out environmental monitoring and tests over the last six years to determine the main causes of deterioration and the potential solutions for conservation.

Cynthia de Giorgio, the curator at St John's Co-Cathedral, said the stone tombs had been damaged by a fluctuation in temperature and humidity levels. The crypt contains the remains of the first 12 Grand Masters who headed the Order between 1522 and 1623, including Grand Master Philippe Villiers de L'Isle Adam and Grand Master Jean de Valette.

The foundation is also restoring a unique set of 29 Flemish tapestries, the carved and gilded walls of the nave, the Chapel of the Blessed Sacrament and the Chapel of Aragon, several major paintings as well as the marble tombstones. The restoration of the cases of the main organ was recently completed.