The discovery of these islands formed no part of Prince Henry’s plan. His desire was to circumnavigate Africa; the expeditions of Perestrello, Zarco, and Tristão Vaz were all intended to sail south and double Cape Bojador, and it was certainly in an attempt to achieve this purpose that Perestrello was driven out to sea to the island of Porto Santo. Many years passed, during which Cape Bojador remained the great obstacle to the Portuguese mariners. Year after year Prince Henry despatched fleets of two or three ships at a time, which sometimes made important discoveries among the islands off the north-west coast of Africa, but they never doubled the great cape. Among these discoveries the most important were the Canary Islands and the Azores. With regard to the former group, the Portuguese were met by a prior claim on the part of Castile; and after a dispute, into the details of which it is not necessary to enter, John the Great, in pursuance of his consistent policy of maintaining peace with Spain, and at the request of Dom Henry, who did not wish to waste his strength in occupying islands, surrendered the Canary Islands to Castile. The Portuguese, however, successfully maintained their claim to the Azores, which still belong to them. This group was first touched at by Bartholomeu Perestrello, the discoverer of Porto Santo, in 1431; and in the following year Gonçalo Velho Cabral discovered the island of Santa Maria. To this captain was allotted the task of further exploring and occupying this cluster of islands; and in 1444 he discovered the island of St. Miguel or St. Michael, where he founded the beautiful little town which gives its name to the St. Michael oranges.