Looking at a somewhat detailed map of the area between The Hague and Leiden in The Netherlands1, you will probably notice that several roads, a few waterways and a railway run more or less parallel to each other and to the coastline.
An impression of this area can be found on this map.
Starting from the A4 (the motorway from The Hague to Amsterdam) and moving towards the coast, you will come across:
De Vliet - a canal connecting Delft and Leiden, believed to have been dug by the Romans.
The Veursestraatweg or N447 - the old Roman road connecting the villages and towns between The Hague and Leiden.
The railway doing pretty much the same thing.
De Schenk - an ancient natural waterway.
De Rijksstraatweg or N44 - forerunner to the A4 motorway and following another ancient track.
Apart from the A4, which was built around 1940, all these features have been around for many centuries. In fact, most of them date from pre-Roman times (though not the railway, obviously). Although the coastline plays a crucial role in this pattern, it is not for the obvious reason that it makes sense to have a road along the coast, rather than at a straight angle to it.
The coast in its present state is lined with sand dunes, varying in height from 10 to 30 metres. The large ones are sometimes called berg, Dutch for 'mountain', showing just how impressive such a small heap of sand can be to the inhabitants of an extremely flat country2.
Nearly 5000 years ago the Dutch coast was located about 10 to 15 miles to the East of its present position. As a result of the last Ice Age, the sea level had been rising rapidly over a period of 4000 years. From 5000 to 2500 years ago, the rise of the sea level slowed down considerably.
The coastline consisted of a single barrier of sand - strandwal in Dutch - cut at various places by the estuaries of small rivers and streams, where tides could flow in and out. The barrier was formed by the combined effort of wind and tides. This situation looked very much like the present Waddenzee, a string of islands with a shallow lagoon-like sea behind them, running along the north coast of The Netherlands and Germany to the west coast of Denmark.
When the rise in the sea level slowed down, the barrier closed and new ridges were formed to the west, giving the impression that the coastline had 'moved' westwards. During this process, several parallel series of sand ridges were formed. The area between the ridges became isolated from the tides and, as a result of rising groundwater, thick layers of peat were formed there. Surplus water collected roughly in the middle of the shallow V-shaped valleys between the ridges, forming the waterways we can still see today.
And Then the Romans Came...
The old sand ridges became popular places for ancient Dutchmen to build their farms and villages. It was the only place where they could keep their feet dry. An old Dutch word for such a piece of dry land is geest. Quite a number of villages and manors in this area derive their name from this: Oegstgeest, Poelgeest and Endegeest.
The peaty areas between the ridges were ideal for grazing cattle and growing crops, while the sand ridges were the most suitable places to build houses and roads on. When the Romans came, they did just that. The area was virtually depopulated when the Romans left, until people started to reappear around the 7th Century AD. Many of today's villages were founded in that period.
Somewhere around the 11th Century AD, the sea level stopped falling and the modern dunes were formed, partly covering the youngest of the old sand ridges. Since the 17th Century, most of the old ridges and some of the young dunes have been levelled to accommodate the Dutch flower bulb industry, especially to the north of Leiden.
Although most of the Dutch coast was formed in this way, the area between The Hague and Leiden is one of the few remaining places where you can see vestiges of the ancient sand ridges.