Sir Robert Dudley (1573-1649), self-styled Duke of Northumberland and Earl of Warwick, was an illegitimate son of the Earl of Leicester, the favourite of Queen Elizabeth, and brother-in-law of the circumnavigator Thomas Cavendish. Through the latter he became a close friend of the sea captains John Davies and Abraham Kendall, both expert mariners. In 1594 and 1595 he sailed to the West Indies, attacking the Spanish and exploring the Guiana coasts. He was a skilled mathematician and navigator himself, and this great work, the Arcano del Mare, one of the greatest atlases of the world, was in part compiled from first-hand experience. On his return to England he took part on Essex' raid on Cadiz in 1596, after which he was knighted. However martimonial difficulties lost him favour at court, and drove him into permanent exile. In 1605 he settled in Florence, became a Roman Catholic, and entered the service of Cosimo II, Grand Duke of Tuscany. He started preparing the Arcano del Mare and employed Antonio Francesco Lucini to engrave the plates. The Arcano del Mare appeared in 1646-47, published in Florence by Francesco Onofri. it was a 6-volume work including 2 volumes of maps and charts and 4 volumes covering the whole field of navigation, astronomical tables, shipbuilding, etc. It was re-issued in 1661 by Guiseppe Cicchini. The cartouches of all but 24 charts in the 1661 edition carry the cypher 'L°6°'.