The Caldicot Level lies to the southeast of Newport between the River Usk and River Wye and consists of 17,500 acres (71 km^2). It is home to Newport Wetlands Reserve. The Wentloog Level lies to the southwest between the River Usk and River Rhymney and consists of 8,500 acres (34 km^2).
The levels are entirely the work of man, having been recurrently inundated and reclaimed from the Severn Estuary since Roman times. They have distinctive patterns of settlement, enclosure and drainage systems belonging to successive periods of use, and are extremely rich archaeologically, with finds from the Mesolithic, Bronze Age and Iron Age periods. They are also an important wetland resource in their own right. Parts have been designated as Sites of Special Scientific Interest. They are also registered as a Historic Landscape of Outstanding Historic Interest in Wales.
One of the most significant finds was of a 3rd century Romano-British boat found at Wilcrick near Magor. The Romans occupied the area from the 2nd to the 4th centuries. In 1878, a boundary stone marking the building of 33 paces of embankment by Roman soldiers was discovered at Goldcliff. Research suggests that, initially, reclamation of the natural saltmarsh for farmland began at a few "island" sites within the marshes, such as at Nash and Redwick, before a sea wall was built along the whole coast.
Goldcliff Priory was established in 1113 and together with other major landowners took responsibility for further drainage work in the area. Settlements became established, linked by droveways such as the Whitewall at Magor, and land was gradually reclaimed for pasture and arable use. A large number of Anglo-Norman sites including castles, churches, court houses, manor houses, moated sites and watermills show near-continuous occupation throughout the Middle Ages.
On 30 January 1607 (New style), floods caused by either a storm surge or a tsunami resulted in the drowning of an estimated 2,000 people, with houses and villages swept away, an estimated of farmland inundated and livestock destroyed. This was one of the worst natural disasters recorded in Britain.
In 1531, Henry VI set up Courts of Sewers to improve drainage, but without any powers to oblige landowners to carry out work. In 1884, the Caldicot and Wentlooge Level Act established a new body, the Monmouthshire Commissioners of Sewers, with responsibility for maintaining sea walls and roads in the Levels. This was superseded by the Caldicot and Wentlooge Levels Drainage Board in 1942.
The pattern of ditches now found on the Caldicot side of the Levels has recently been significantly complicated by the construction of the Newport Wetlands Reserve. Whereas the raison d'etre of all previous reens and ditches had been to drain the land, the aim of the network of new waterways constructed as part of the reserve has been to keep the land flooded, albeit with fresh water