Romney Marsh is a sparsely populated wetland area in the counties of Kent and East Sussex in the south-east of England. It covers about 100 square miles (260 km2). The Marsh has been in use for centuries, though its inhabitants commonly suffered from malaria until the 18th century. Due to its location, geography and isolation, it was a smuggler's paradise between the 1600s and 1800s. The area has long been used for sheep pasture: Romney Marsh sheep are considered one of the most successful and important sheep breeds. Criss-crossed with numerous waterways, and with some areas lying below sea level, the Marsh has over time sustained a gradual level of reclamation, both through natural causes and by human intervention.