Up to the fifteenth century the inhabitants of the Iberian Peninsula were chiefly occupied in slowly moving back the tide of Mohammedan conquest, which had spread nearly throughout the country from 711 onwards. The last sigh of the Moor in Spain was to be uttered in 1492--an epoch-making year, both in history and in geography. But Portugal, the western side of the peninsula, had got rid of her Moors at a much earlier date--more that 200 years before--though she found it difficult to preserve her independence from the neighbouring kingdom of Castile. The attempt of King Juan of Castile to conquer the country was repelled by João, a natural son of the preceding king of Portugal, and in 1385 he became king, and freed Portugal from any danger on the side of Castile by his victory at Aljubarrota. He married Philippa, daughter of John of Gaunt; and his third son, Henry, was destined to be the means of revolutionising men's views of the inhabited globe. He first showed his mettle in the capture of Ceuta, opposite Gibraltar, at the time of the battle of Agincourt, 1415, and by this means he first planted the Portuguese banner on the Moorish coast. This contact with the Moors may possibly have first suggested to Prince Henry the idea of planting similar factory-fortresses among the Mussulmans of India; but, whatever the cause, he began, from about the year 1418, to devote all his thoughts and attention to the possibility of reaching India otherwise than through the known routes, and for that purpose established himself on the rocky promontory of Sagres, almost the most western spot on the continent of Europe. Here he established an observatory, and a seminary for the training of theoretical and practical navigators. He summoned thither astronomers and cartographers and skilled seamen, while he caused stouter and larger vessels to be built for the express purpose of exploration. He perfected the astrolabe (the clumsy predecessor of the modern sextant) by which the latitude could be with some accuracy determined; and he equipped all his ships with the compass, by which their steering was entirely determined. He brought from Majorca (which, as we have seen, was the centre of practical map-making in the fourteenth century) one Mestre Jacme, "a man very skilful in the art of navigation, and in the making of maps and instruments." With his aid, and doubtless that of others, he set himself to study the problem of the possibility of a sea voyage to India round the coast of Africa. [Illustration: PROGRESS OF PORTUGUESE DISCOVERY]