The Tidal mills were first used during the seventh century in the medieval Europe and they are considered as one of the great examples of improving Middle Ages technology. A tidal mill is a special type of water mill which is driven by the rise and fall of tides. In order to use them, a dam with a sluice was used to be created across a proper tidal inlet.
They could also be used at a section of a river estuary made into a reservoir. With the upcoming tides, the water used to enter the mill pond through a one-way-gate. This gate was used to get automatically closed as the tidal began to fall. With the lowering tide, the stored water could be released to turn a water wheel.