St John's Co-Cathedral, in Valletta, is teeming with life... Tourists are streaming through, taking in its splendour, aided by equipment held tightly to their ears for a guided tour around this gem of architecture. On their way out, satisfied and mesmerised, they drop it off at the custodians, who cordially wish them a good holiday in the appropriate language.

In the shoulder months, up to 500 visitors a day can tread the jewel of a floor that paves the co-cathedral - a figure that could increase to 2,000 in summer. That would be way too many footsteps, consistently wearing away the registered 405 invaluable tombstones, dating back to the 17th century, that tile its floor - footsteps that have caused irreparable erosion through abrasion over the years...

But not anymore!

Today - and for the past weeks - a hi-tech carpet, costing close to Lm20,000 and covering the walkways, separates the feet from the marble, protecting it from further deterioration.

It was the first mission St John's Co-Cathedral curator Cynthia de Giorgio embarked on since she took up her position two years ago. And it was a long procedure: a whole year of research into the most ideal carpeting, which came all the way from the US and promises to not only protect the priceless floor from footsteps, but also to counteract rising damp, allowing water vapour to dry off and escape.

The supplier, 3M, which specialises in protective carpets, was engaged to produce a specific type, known as open web, which is made of a vinyl filament, pressed into a mesh, Ms de Giorgio explains.

"Unfortunately, you never really know what the best solution is, but this is the best for the moment. Perhaps, in 20 years' time there may be something else. The good thing is, however, that the carpet is non-invasive and can be removed if a better solution is found. It is definitely not going to cause any damage.

"It was my priority. The tombstones are so unique; I've never seen a floor like this anywhere in the world. Because of the deterioration it was suffering, I felt something had to be done quickly. It is never too late for conservation."

The tombstones are, doubtless, one of the main attractions of St John's, but the ordinary visitor need not see all 405 of them. Walkways of carpeting have, therefore, been created, in no way detracting from the co-cathedral's rich interior.

A result of a tradition of the Catholic faith, whereby people were buried within a church, the tombstones are made of a large marble slab, with a design carved out and filled with coloured marble inlay. It is their polychromy that renders them even more unique, Ms de Giorgio maintains.

The two types of damage the tombstones have suffered over the years include erosion by abrasion - the worst, as it cannot be replaced - and the breaking of the marble.

"The marble of the design is slim. When you step on it, it can crack, and small pieces start lifting off and get lost. Marble is considered to be a hard material, but it is also brittle. Once it starts breaking, it can vanish within weeks," she warns.

That is where the work of the two full-time marmisti comes in. Raymond Aquilina and Jesmond Bartolo are employed to take care of the co-cathedral's marble - and there is plenty! Matching the missing pieces is no mean feat; a lot of it is hundreds of years old. Besides, every piece of marble replaced has to be documented. A record of what has been changed and what is original has to be kept.

Two full-time marmisti would seem to be adequate, if not excessive, at first glance. But in reality - and despite their great dedication - they are almost not enough. Mr Aquilina spends his entire day restoring the tombstones - a job he knows is bound to last his lifetime. But he is not put off by its magnitude and the meticulous work it entails. In fact, he has just finished the mammoth six-month job of laboriously cleaning the 16 pilasters of the co-cathedral. They were so dirty the coats of arms on the top were thought to be flat. But when they were cleaned, it was discovered they were actually in relief.

"The result is fantastic," says Ms de Giorgio, pointing out the shining verde antico marble.

Ms de Giorgio holds the tombstones to heart and is out to do her part to preserve them - also for their artistic beauty. The designs are so rich in symbolism, they have been the subject of intense study, covering a wide spectrum of artistic styles. After all, the earliest tombstones date back to 1608 and the latest to the first decades of the 19th century, Ms de Giorgio highlights.

"Usually, a monument belongs to one period, but this is one of the rare ones that spans a variety of styles," she says.

The next step would be to find a temporary solution to the seating problem, tackling the chairs in the nave, which also cause their fair share of damage. The idea would be to trim down large functions.

"Think about it - when St John's is packed solid, every tombstone takes about nine chairs. That would be 36 pressure points and lots of weight. Pressure is pressure, and the only way to relieve it is to remove it."

Considering the tombstones have been around for so long, they are still in a relatively good state of preservation. After all, the co-cathedral was never opened to thousands of visitors and was only for the use of the Knights, Ms de Giorgio says.

However, today, every important Mass - and there are many - is held there, and she has some reservations about that.

Other projects in hand, on the initiative of the St John's Co-Cathedral Foundation, include the restoration of the Triumphal Arches. They are being cleaned of the grime and grit that has accumulated over the past 200 years, and are being re-gilded. The whole project should take two years, but the first two arches are expected to be ready in two months.

The tapestries - one of the largest collections in the world, counting 29, woven in Brussels, based on the Rubens cartoons - are being restored in Belgium.