The Story of Norway by Hjalmar Hjorth Boysen

In accordance with established custom, the three sons of Magnus Barefoot were proclaimed kings, and the land was divided between them. There is, however, a probability that this division pertained chiefly to the royal estates, from which the kings derived their principal revenue, but did not involve a division of the country itself into separate kingdoms. Eystein was at the time of his proclamation fourteen years old, Sigurd thirteen, and Olaf three or four. They were all illegitimate, but had been acknowledged by their father. There was, at that time, a great agitation throughout Europe on account of the crusades. Kings, knights, and even children, in their anxiety to save their souls, threw reason to the winds, and, relying upon supernatural aid, started with insufficient preparations on adventurous undertakings. This grand religious enthusiasm did not reach the North until its force was partly spent.

Some of the men who had visited Jerusalem returned home, but apparently were but little affected by religious phases of the war against the unbelievers. They talked rather of the chances for worldly fame and gain which the crusade presented, and aroused a desire in many of their countrymen to win both heavenly and earthly glory by an expedition to the Holy Land. It was the general desire that one of the princes should command the expedition, and Sigurd, who had inherited his father's spirit, willingly consented. In order to fit himself out properly he needed money, and this he could not get without the good-will of the people.