The deltas of the rivers Rhine, Meuse (Dutch: Maas), and Scheldt (Dutch: Schelde; French: Escaut) are connected so intimately that it is impossible to trace exact boundaries between them. Together they form a strip of Holocene deposits (clay, sand and peat), about 50 km wide, lying between the North Sea to the west and northwest and the Pleistocene region of the Netherlands to the east and southeast. The delta of the river Scheldt is the southern part of the joint deltas of the three rivers; it is nearly identical with the present province Zealand of the Netherlands. Secular fluctuations of the average level of the sea in relation to the land, both positive and negative, together with sedimentation and erosion, from the earliest times onward to the present day, continuously modified the local boundaries between land and water. The changing influx of salt water and the rate of drainage of the land always deeply influenced the vegetation and the whole character of the region. Moreover, since the Roman occupation in the beginning of our era, man had an ever increasing influence on the course of the river branches and on the water level in the rivers and ditches.