ON a windswept plain 35 miles north of Lisbon stands one of Europe’s great white elephants.

It was built by King João V to fulfil his promise that he would build a monastery if he received an heir. The King of Portugal had married Dona Maria of Austria in 1708 and three years later she was still childless. Then the King made his pledge and a daughter, Dona Maria Barbara, later Queen of Spain, was born the same year, in 1711.

The foundation stone of the monastery was laid in November 1717. At the time, Portugal was beginning to receive gold from new mines being opened up in what was to become the state of Minas Gerais (literally "general mines") in Brazil. And with this new spectacular wealth arriving in ships up the Tejo estuary for all the country’s capital and for all of Portugal’s rivals to see King João V planned that the Convent of Mafra should be a monastery to rival the vast Escorial just outside Madrid.

Plans for the construction of this great edifice were drawn up in Rome by Johann Friedrich Ludwig of Ratisbon and he was to engineer the vast building and supervise its construction.

Almost all the master carpenters, master builders, master masons, sculptors and artists were Italian. Materials came from Italy, France, Brazil and Flanders. Thus the gold that came from Brazil passed through Portuguese hands to enrich other nations. The Portuguese contribution to Mafra was restricted to paying the bills as big as the building - some 48 million cruzados enough to seriously weaken the country’s economy - and to supply the workforce.

A total of 50,000 people toiled on the Convent of Mafra during the height of construction, using 1270 cattle to pull carts bringing materials, including the marble and the limestone blocks.

Seven thousand handcarts were used. A force of over 7000 soldiers supervised this vast army of compulsory labourers. The combined total of so many workers (and cooks and workcamp attendants) absent from productive work in the fields, vineyards and in the town and villages crippled the regular economy of the country. A total of 1383 people died during the construction.

The building of Mafra, including a huge basilica and royal palace, took 17 years. The church was dedicated in 1730 during a service lasting eight hours. The Convent and palace were not finished until 1735.

Without doubt, the Convent (and palace complex) is one of the grandest and most sumptuous in Portugal: 220 metres in length along the front, covering 40,000 square metres, with a total of 880 rooms and 4500 doors and windows.

The church of Nossa Senhora and Santo António de Mafra is the central building of the whole complex and was modelled after St Peter’s and the Church of Jesus in Rome. Eighteen huge Italian statues stand outside and there are a further 40 Italian statues inside the airy, cool church. A notice inside the church does not seem to appreciate the irony when it declares that Mafra has the best collection of Italian 18th century sculpture in Portugal.

The vital statistics of the basilica speak of the scale of the whole complex of Mafra: the dome stands 65 metres high from the floor, is 13 metres in diameter and took two and a half years to build. The church is just short of 60 metres long and 43 metres at the crossing.

However, this enormous size is reduced, almost miniaturized, to feel on a human scale, by tricks of light and by our own eyes, by the abundance of different colours and different shapes of limestone and marble. Here is pink, white, blue , yellow, red, grey and black. The effect is to break up the preposterous and monotonous scale, especially after the dull main façade facing the modern little town of Mafra.

The basilica has 11 chapels and six organs, with a total of 24 pipes. However it is more famous for its bells. The Convent of Mafra has the largest "orchestra" of bells anywhere in the world; 57 bells in each of the two towers. Forty-eight of these were cast in Liege and Antwerp in 1730. The biggest bell weighs 10 tonnes. The smallest weighs 30 kilogrammes. Each summer, a one-hour bell concert is performed on Sundays at 4pm.

One of the most beautiful parts of the whole complex is the library - built to house some 80,000 volumes. The rococco room - at 88 metres long, the longest in the whole complex - is a waking dream of ivory light, gilded decoration and shinning marble floor of varied colours.

The other rooms of the palace feel dull to the senses by comparision. Perhaps it is all just too much: so big now so empty and yet still confining.

Mafra feels like the setting for a comic opera. It is certainly the setting for Portuguese Nobel prize winner José Saramago’s "Balthazar and Blimunda."

The convent is open six days a week (closed Tuesday) from 10am to 5pm. Visits are only by guided tour.

By Steve English