Leeds was a small manorial borough in the 13th century, becoming a major centre for the production and trading of wool in the 17th and 18th centuries, then a major mill town during the Industrial Revolution; wool was still the dominant industry, but flax, engineering, iron foundries, printing, and other industries were also important. From being a market town in the valley of the River Aire in the 16th century, Leeds expanded and absorbed the surrounding villages to become a populous urban centre by the mid-20th century.