The Stone Lock is one of the most interesting hydraulic engineering objects in Poland. It was built in the years 1619-1623 and designed by Jan Strakowski based on plans developed by the Dutchmen from Alkmaar: Willem Jansen Bening and Adriaen Olbrantsen. One of the purposes of constructing the structure was to power the city mill, which served a very important role as a backup mill. The enemy could easily disable the mills of the Old Town by blocking the Radunia Canal. With the originally wooden gates of the lock, and since the 19th century, metal gates, it was possible to artificially raise the water level in the Vistula Delta, causing a "controlled" flood, or to protect the city from seawater that would be pushed into the Motława during storms. On the stone embankments, you can see four decorative turrets, which, apart from their visual value, also served defensive functions to prevent enemy soldiers from crossing the embankments and taking the bridge. At the end, there is a so-called ravelin, a small bastion built in the 17th century. In 1656, the Swedish army abandoned the siege after the flooding of the Gdańsk's outer defenses.