Roughly one-fourth of the Netherlands lies below sea level -- including large parts of Rotterdam and Amsterdam.

Dams had protected farmland from the sea since at least the Roman times, but large-scale building of dikes occurred around 1,000 AD, when people began draining marshland to farm and mine for energy-rich peat. At one point, the country had over 1,200 miles of dikes, and men could be called upon at any time to shore up these defenses in what was known as the "dike army."

In more modern times, other engineering projects like sea walls and flood gates have reduced the need for dikes, though the Dutch have continued to reclaim large swaths of land from the sea or lakes. Indeed, Amsterdam's airport lies in what used to be a lake.

As the saying goes, "God created the earth, but the Dutch created Holland."