Wooden treadmill cranes for heavy lifting

For unloading heavy cargo - like barrels of wine or blocks of stone - from ships, treadmill cranes were used.  Smaller cargo was carried off the ship.  The picture below is a reconstruction of such a treadmill crane.  It was built for Bruges 2002, when the city was the cultural capital of Europe.  The crane is still on display in the Wulpenstraat near the ringroad.
In the 16th century two such cranes were in use in Bruges.  Two to four men were used to operate the crane, depending on the load.  The crane could lift up to a ton.

You can read about the history of the crane on the link below.

http://www.regiobrugge.be/tourist/brugsetredmolen.php

In Mechelen a similar type of crane was used.  It was first mentioned in 1311, renewed several times and finally taken out of service in 1887.  From the 19th century a painting and pictures still exist.  It was located on the Haverwerf and the adjacent bridge over the Dijle river was named after it, i.e. Kraanbrug or Crane Bridge.

The mechanism of the cranes is fairly simple.  A rope coils and uncoils around the axis of the crane by the turns of the treadmills.  The rope runs over a pulley.  There is no mechanism for leverage, such as cogwheels or a block and tackle mechanism.  The crane itself could be turned by a beam at the backside.

Another example of a still-existing treadmill crane can be seen in the Crane Chamber of the Sint-Romboutstower at Mechelen.  Three persons could walk next to each other to operate the crane.