Koppelpoort

The Koppelpoort is a medieval gate in the Dutch city of Amersfoort, province of Utrecht.

Completed around 1425, it combines land and water-gates, and is part of the second city wall of Amersfoort, which was constructed between 1380 and 1450.

The gate was opened and closed every day by the appointed raddraaiers, "wheel-turners".

It was an extremely dangerous task; if they did not begin walking simultaneously, then one could fall, dragging the rest along with often fatal results.

While the gate was going down, walking in the wheel grew ever easier and faster, and many people stumbled and broke their limbs.