John is often remembered as one of the greatest patrons of the arts in Portuguese history, having commissioned numerous construction projects and artistic studies. The king's most famous and important work was the Royal Palace-Convent of Mafra. In early 1711, married to Maria Anna of Austria for three years and without an heir, John grew worried for the future of the House of Braganza. He met with D. Nuno da Cunha e Ataíde, High-Inquisitor of Portugal, who assured the king that if he promised to build a convent for Franciscans in Mafra, in the Lisbon countryside, Maria Anna would bear him a child by the end of 1711. John agreed to do so. Construction started in 1717, with plans for a modest church convent for one hundred friars. However, in the following years, with a gratuitous flow of gold from slave labour in the American colonies of Brazil and Maranhão, the plans were altered to become a "magnum opus" of John's reign, accommodating three hundred friars and adjusted to become a hybrid convent-palace, including a royal library, a basilica, and a vast set of apartments for the royal family. Noting the vast size and scope of the project, Charles de Merveilleux, a Swiss nobleman living in Portugal in 1726, remarked that "King John has decided to build a second Escorial."