The Dunkirk transgressions were tidal bulges or other sea level-related marine transgressions (risings), often heightened by river floods, affecting the North Sea and adjoining low land. Most of this land is vulnerable to such events being below or approximately at sea level. Three events and mass evacuations, at least, are seen, some stretching to land above-sea level today. The events affected the Low Countries and other land near the German Bight, Thames Estuary and The Wash. They spanned from the late Roman period until Early Medieval Europe.