In Roman times, this northernmost branch of the Rhinedelta was the main distributary of this major European river. Along its banks the Romans built their frontier castella part of the Limes Germanicus.
Since the Middle Ages, however, the stream lost its importance as it silted up, and eventually it is nearly cut off from the Nederrijn-Lek main artery. Yet it retained the name "Rhine".
Originally, the city of Utrecht was built by the Romans at a ford near the place where the Kromme Rijn forks into rivers Vecht (north) and Leidse Rijn (west); the last stretch within the city walls, however, was channelised to form the Oudegrachtcanal. Rivers Leidse Rijn and Vecht extend from the city moat and are the continuation of the Kromme Rijn.
Satellite image of the central part of the Rhine-Meuse delta showing the city of Utrecht and its surroundings, including the Kromme Rijn branch (b), which forks from the Nederrijn-Lek main artery at Wijk bij Duurstede (just outside this image, to the east of the rightmost number 2).