Niebla's ramparts dating from the time of the Almohads (a Berber dynasty reigning over Andalucía in the 12C) were built with clay from the banks of the Río Tinto. This explains their reddish colour, which is particularly lovely when lit by the rays of the sun. The walls are more than 2km long, with 50 towers and five gateways. They are one of the most complete sets of walls in Spain.