The intimacy maintained by Frederick with Mohammedan sovereigns contributed greatly to the prosperity of his dominions. The Sultan of Egypt was his friend. The Emir of Tunis was his tributary. With the other Moslem princes he was on the best of terms. Treaties of commerce, framed for mutual advantage, were frequently negotiated with these potentates, who were only too willing to discriminate against other European monarchs in favor of the Emperor of Germany. In 1241, on the arrival of the Imperial ambassadors, Cairo was illuminated in their honor. The trade of Sicily extended to India. The luxuries of the Orient were brought to the ports of Palermo and Messina. In their markets the arms, the jewels, the stuffs, the porcelain, of countries remote from civilization found a ready sale. In return, immense quantities of grain and manufactured articles were exported. It has been established upon undoubted authority that white female slaves of Christian birth formed no inconsiderable portion of the commodities dealt in by the subjects of Frederick II. The fortunate geographical situation of Sicily, her magnificent harbors, the productiveness of her soil, the excellence and variety of her manufactures, had, in all ages, been factors of paramount importance in her commercial development. That development was now materially aided by the reciprocal observance of humane and courteous regulations, hitherto unrecognized in the intercourse of nations during the Middle Ages. Merchants in foreign ports were received with lavish hospitality; distrust of strangers gradually subsided; and unfortunates, cast away at sea, were no longer compelled to endure both the violence of the elements and the heartless rapacity of ferocious outlaws or amateur freebooters. In the widely distributed commerce of the monarchy the crown enjoyed no insignificant share. The ships of Frederick were anchored in every harbor; his warehouses were filled with the choicest and most costly fabrics of every country; and his agents, conspicuous for their enterprise and daring, collected, in the distant and almost unknown regions of the Orient, articles whose sale would most contribute to the benefit of the royal treasury. The principles of free trade seem to have been first promulgated in the maritime code of Sicily. The Emperor, however, in the application of those principles, evinced no reluctance in discriminating against his own subjects, whose vessels were not permitted to clear for foreign ports until those of the crown had been a certain time at sea. Every branch of commerce paid tribute to the imperial merchant. His ships carried pilgrims to the Holy Land. The grain he annually sent to Africa returned an enormous and certain profit. His trade with India brought into European markets objects of unfamiliar uses and elaborate workmanship, whose rarity often increased their great intrinsic value. His friendly relations with Mohammedan princes, begun during