From the World Heritage inscription:
Valletta is pre-eminently an ideal creation of the late Renaissance with its uniform urban plan, inspired by neo-Platonic principles, its fortified and bastioned walls modelled around the natural site, and the voluntary implantation of great monuments in well-chosen locations.
The capital of Malta is one of the rare urban inhabited sites that has preserved in near entirety its original features. It is inextricably linked to the history of the military and charitable Order of St John of Jerusalem. It was ruled successively by the Phoenicians, Greeks, Carthaginians, Romans, Byzantines, Arabs and the Order of the Knights of St John. The city has undergone no important modifications since 1798, the date when it was abandoned by the Knights of St John.
Within the confines of the fortified peninsula of Valletta, which constitutes one of the most attractive natural sites of the Mediterranean, dominating the two ports of Grand Harbour and Marsamxett Harbour, the density of the buildings dating from the 16th, 17th and 18th centuries is impressive. After the great siege of Malta in 1565, the new city, based on an orthogonal urban plan, was founded by the Italian engineer Francesco Laparelli of Cortona (1521-70), the planning being carried out by Girolamo Cassar. The fortification and the uniform urban plan of Valletta were inspired by architectural principles of the Italian Renaissance in combination with techniques of contemporary city-planning and aesthetic considerations of urban theorists. The buildings of the order are harmoniously integrated within the uniform grille of the streets: the Cathedral of St John (former Conventual Church of the Order, 1573), Palace of the Grand Master (end of 16th century), Auberge de Castille et Leon (1574), Auberge de Provence (1571-75), Auberge d’Italie (1574), Auberge d’Aragon (end of 16th century) and Infirmary of the Order (end of 16th century).
The same is true of the great religious buildings as Our Lady of Victory (1566), St Catherine (1576), and Il Gesù (1595). The improvements attributed to the military engineers and architects of the 18th century have not disturbed this harmony (Auberge de Bavière, Church of the Shipwreck of St Paul, Library and Mantel Theatre, etc.). The total of 320 historic monuments within a confined area of 55 ha is among the most strongly concentrated of this nature in the world.
The city of Valletta has seen a great deal of history. The moment you walk into the city past its enormous walls, you can see why this fortress why so important to the history of the Mediterranean.
While the site has been inhabited for thousands of years, most of what you will see in Valletta dates from the 16th century to today. The Knights of Malta were responsible for much of the construction in the city. The Siege of Malta during WWII also destroyed many buildings which lead to wide scale reconstruction after the war.
St. John’s cathedral is one of the more splendid cathedrals you will find in all of Europe. (image above) The interior is gilded in gold and the floor is covered with the tombs of many of the distinguished knights of the order. The biggest attraction, however, is The Beheading of Saint John the Baptist by Caravaggio.
One event you should observe is the noon salute at the salute battery. It is a cannon which is fired every at noon every day. You can watch it from a balcony for free or from within the battery for 2 Euros.
Expect to spend at least a half day in Valletta if not a full day. As the capital city of Malta it is easy to reach and explore on foot.