side of the passage in 1626, while two watermills with five systems of mill wheels each flanked the still undeveloped watercourse. Ships, still pulled by hand over the shallow passage, couldn't pass at all during some seasons and regularly ran ashore causing constant and expensive repairs, while the sheds and simple buildings next to it were often washed away by floods in spring and autumn. Lock of Queen Christina In 1634, works were begun to transform the two streams into a modern canal and construction works on the lock could finally start when the two oldest towers were demolished in 1637. Dutch craftsmen were brought in for the project led by two Dutch carpenters, called Adrian Dams and Lennart Hermanson. A pole-driver was used to dam up the watercourse during four months before the seabed was excavated and larger blocks were burnt into smaller pieces carried away by hand. Finally, in 1638 the dam was temporarily opened for the wooden box of the canal, towed in from the construction site on Skeppsholmen. The interior faces of the box was then dressed up in a block wall using stone imported from the Netherlands before the copper-dressed locks were completed. When completed in 1642, the Dutch were sent home and the lock was named Drottning Kristinas sluss ("Lock of Queen Christina") after Queen Christina (1626–1689), about to come of age. In spite of the constant need of repair, the canal and its lock was an instant success, the city's earnings from customs increased sixfold, and as the loading an unloading of iron was relocated to the old moat in 1662, the area developed into one of the most vital ports in Europe, after 1636 handling approximately two-thirds of the Swedish export. German and Dutch merchants opened branch offices on the southern side in 1664, and Russian shops were built next to them in 1641 (the space is still called Ryssgården, "The Russian Yard"). A planned Swedish trade house, started by Nicodemus Tessin the Elder, half-finished and struck by fire in 1680, was finally completed to the plans of Nicodemus Tessin the Younger and called the "Southern Town Hall" (Södra Stadshuset), today housing the Stockholm City Museum. In 1698, Tessin the Younger added a second drawbridge to the area, demolishing most of the tower of Gustav Vasa and the moat in the process. The southern city gate had by this time transformed into