Danish straits

The Copenhagen Convention of 1857 made all the Danish straits open to commercial shipping.

Where an island is situated between a "belt" and a "sound", typically the broader strait is called "belt" and the narrower one is the "sound": During the 20th and 21st centuries the surrounding areas grew in population and cross-border trade developed, particularly as part of the European single market.

Ferries crossed many of the straits but some of these have been replaced with fixed links to reduce journey times.

The fixed links include: The Germanic word "sound" has the same root as the verb to sunder in the meaning of "to separate".

Another explanation derives "sound" from an ancient verb "sund" in the meaning of to swim.