In 1602 the Danish king, worried about the activities of English and German ships in what he considered to be territorial waters, instituted a trade monopoly in Iceland, restricting commerce to Danish merchants. They were required to regularly send merchant ships to Iceland carrying trade goods needed by the country. While illegal trade flourished in the 17th century, from 1685 the government instituted stricter measures to enforce the monopoly. It flourished until 1787. As a result, Iceland farmers grew a type of rye predominant in Denmark, and brennivín, an akvavit produced from rye, was introduced. These products displaced other cereals and beer.