Koppelpoort, Amersfoort, province of Utrecht, Netherlands.... www.castlesandmanorhouses.com .... The Koppelpoort is a medieval gate built around 1425. It combines land- and water-gates, and is part of the second city wall constructed between 1380 and 1450. The gate was opened every morning and closed every night by the appointed raddraaiers, "wheel-turners". A minimum of twelve wheel-turners were press-ganged to operate giant hamster-wheels.