Have you ever wondered how Valletta and the Three Cities would have looked like had no lines of fortifications been built?

Was it Muslim slaves who built most of these lines of defence? And who were the men who designed and built such magnificent shields of stone to safeguard the lives of the inhabitants in case of attack?

These and 1,001 other questions are answered in a highly-illustrated book called The Art Of Fortress Building In Hospitaller Malta authored by Stephen C. Spiteri.

In this book, put together over the past 22 years, Dr Spiteri, Superintendent of Fortifications at the Ministry for Resources and Rural Affairs, notes that the Knights of the Order of St John needed three elements to turn Malta into an island fortress: money, materials and knowhow.

"The knights found an ample supply of stone and a fine building tradition but, in 1530, they lacked the organisation capability to carry out works on a grand scale that the bastioned enceintes required. Throughout most of the 16th century, the labour force was in short supply".

So labour was imported from Sicily. In order to entice workers, the knights used to advertise that they paid workers well and on time.

There were about 4,000 workers employed in the building of Valletta in 1566, the largest workforce ever assembled for any one project at the time.

"It is a gross misconception that the bastions were built by Muslim slaves. The slaves, no more than about 2,000 at any one time, with 600 of them employed on the Order's galleys, of whom only a fraction were put to work on bastions when the islands were not facing some national emergency, were generally charged with removing and carting soil and rubble.

"The cutting and shaping of stone and the building of revetments and ramparts were carried out by private contractors known as capomastri who had their own gangs of skilled workers, with such work being given out on contract," Dr Spiteri said.

Being a rocky island, Malta gave military engineers the chance to hew fortresses out of the live rock. This gave fortresses tremendous strength, while cutting the ditch around them provided the stone needed to build the fortresses themselves.

From the 16th century onwards, when the threat of war had subsided to a large degree, monumental architecture predominated through baroque influences. Often, the knights cut corners. For example, to save money, they used soil instead of lime as a binding agent in the construction of ramparts. That is why so many wild plants and sometimes trees grow on the walls.

The men who built these effective war machines were military engineers, being both architects and soldiers. By inviting to Malta the leading experts of their time, the knights were effectively importing the latest in fortress ideas and technology. That is why Malta's fortifications are a unique example of the best the European schools of military architecture had to offer.

The Art Of Fortress Building In Hospitaller Malta, published by BDL, joins a growing literature that draws attention to the uniqueness and importance of this heritage and a growing concern about its preservation.

"We have to find imaginative and productive but sympathetic uses for these fortifications if they are to remain valid elements of our historical and cultural patrimony. What is clear is that they cannot all be used as museums. One model I like is the concept of the Spanish parador," Dr Spiteri said. Parador hotels offer accommodation in castles, palaces, fortresses, convents, monasteries and other historic buildings.

Dr Spiteri has animated the book, like his other tomes, with a high visual content. This richness of design gives readers, most of whom, as one rightly expects, are not likely to be military engineers, the chance to understand, at a glance, the ingenious and inventive elements behind fortress building.