The site was not empty before Smidt arrived, only unpromising. Lehe existed by the twelfth century and Geestendorf appears in ninth-century documents — tiny villages raised on islands in a swampy estuary. Bremen had claimed de facto rule of the lower Weser since 1381, which is why Swedish troops from Bremen-Verden seized Bremerlehe by force in 1653, and why the First Bremian War followed in 1654 and cost Bremen the place entirely. In 1672 Swedish colonists tried to plant an unfinished fortress here, Carlsburg, meant to protect and to control shipping headed upriver. A century and a half later Bremen simply bought the same ground back and built the harbour the fortress had been meant to guard. Hanover responded by founding a rival town across the Geeste, Geestemünde, in 1845. The two grew up alongside each other on the same three pillars: trade, shipbuilding and fish.

In 1854 alone, 76,875 people left Europe through Bremerhaven, and by that year it was the largest emigration port on the continent. Between 1830 and 1974, roughly seven million departed from these quays. They were mostly Germans, but also Poles, Russians and Scandinavians who had crossed half a continent to reach the water — leaving because of failed harvests, failed revolutions, conscription, debt, or because a brother had gone ahead and written back. For nearly all of them this dock was the last piece of Europe they ever stood on. The German Emigration Center opened on the site on 8 August 2005, designed by Andreas Heller, and it does something museums rarely manage: it hands each visitor a real emigrant's biography and walks them through reconstructed spaces — the quay at night, the steerage berth, the arrival hall — following that one person. Its Galerie der 7 Millionen puts faces against the number. It was named European Museum of the Year in 2007, and in April 2012 added a wing on the other direction of travel, three centuries of immigration into Germany.

Liners kept getting bigger and locking them in and out cost hours, so in 1927 the Columbuskaje was built directly on the Weser bank, with the Columbusbahnhof beside it — a railway station on the pier, running passengers straight from carriage to gangway. It is a cruise terminal now, the Columbus Cruise Center, and the traffic largely comes back these days rather than leaving for good. Older than any of it, and still working, is the Bremerhaven Lighthouse: a brick Gothic tower built between 1853 and 1855 to a design by the Bremen architect Simon Loschen, 37 metres tall, the oldest operating lighthouse on the German North Sea mainland. It still serves as the rear light of a leading pair guiding ships down the Weser. Every five years the harbour fills for Sail Bremerhaven, an edition of which drew more than 270 vessels and 3,500 crew in 2015.

Bremerhaven has very few old buildings, and there is a reason. As one of the Kriegsmarine's most important North Sea bases it was heavily bombed, and 79 percent of the city was destroyed — the raid of 18 September 1944 left the inner city largely in ruins. Key parts of the port were deliberately spared so the Allies would have a working harbour afterwards, and postwar Bremerhaven became a United States enclave inside the British zone; American forces stayed at the Carl Schurz Kaserne until 1993. The city returned to Bremen in 1947 and took back its name. What visitors see today is new on purpose. The Havenwelten waterfront gathers the Klimahaus of 2009, which walks you along the eighth meridian of longitude through every climate that line crosses, and the German Maritime Museum, built by Hans Scharoun in 1975 around the Hanse cog of 1380 that was dug out of the Weser mud at Bremen in 1962. A museum harbour holds the Type XXI submarine Wilhelm Bauer and the salvage tug Seefalke of 1924.

Fischereihafen I was finished at Geestemünde in 1896, and fishing became the city's third industry and its identity; Frosta and the restaurant chain Nordsee are headquartered here. Modern trade is measured differently. The Stromkaje container quay runs almost five kilometres, making Bremerhaven the sixteenth-largest container port in the world and the fourth-largest in Europe, with 5.5 million TEU handled in 2015. More than two million cars pass through the wet docks every year — 2.3 million in 2014 — more than any other city in Europe, and BLG Logistics runs the continent's largest car transshipment centre here. In 2011 a new panamax lock replaced the Kaiserschleuse of 1897, itself the largest lock in the world when it opened. Alongside all that commerce sits the Alfred Wegener Institute, founded in 1980 and named for the geophysicist who first argued that the continents move: from this river mouth, German polar and marine research runs to both ends of the Earth.