For most of its first two centuries as a port, Belfast had a problem: the lough was too shallow and the channel curved too much. Ships arriving from the Irish Sea couldn't reach the quays fully loaded. They had to anchor downstream at a place called Garmoyle and lighten their cargo into smaller boats - paying twice for unloading, paying again for Customs supervision, losing time on every tide. By 1785 the trade was busy enough that Parliament constituted a Ballast Board to fix things, but the real change came under the Victorians. Engineers began straightening the river in 1839, slicing through bends, dredging a deep cut they would call the Victoria Channel. It opened in 1849, and suddenly Belfast had what Belfast had always needed: water deep enough for the world.

The reclaimed land that emerged from all that dredging became Queen's Island, and on Queen's Island a shipyard called Harland and Wolff laid the keel for a vessel they numbered 401. She would be launched in 1911 and christened RMS Titanic. The yard built her sister Olympic alongside her, and her younger sister Britannic after, under the world's largest gantry crane. Today the gantries Samson and Goliath still loom over the same slipways, painted yellow, visible from the city centre and from passenger jets descending into George Best Belfast City Airport, which now occupies a strip of the same harbour estate. The Titanic story sank in the North Atlantic, but the dock she was fitted out in - a basin so vast it can hold modern oil tankers - is still there, water still in it, walls still vertical, the largest dry dock in the world when it was new.

Most ports become museums of themselves. Belfast did not. The harbour today moves around 24 million tonnes of cargo a year, handles roughly two-thirds of Northern Ireland's seaborne trade, and is one of only two ports on the island that takes every type of freight: containers, dry bulk, liquid bulk, break-bulk, rolling freight, passenger ferries, cruise ships. Stena Line's super-ferries to Cairnryan and Birkenhead carry over a million passengers a year and well over half a million trucks. Eight remote-controlled gantry cranes, delivered in late 2019, lift containers off feeder ships from Rotterdam and Antwerp. Over 700 firms employing 23,000 people work within the harbour estate. It is the kind of place where the past is not curated; it just keeps operating alongside the present.

Tucked into Alexandra Dock, painted in dazzle camouflage, sits a small grey ship called HMS Caroline. She is a light cruiser built in 1914, and she fought at the Battle of Jutland - the largest naval engagement of the First World War. After the war she became a training ship, then headquarters of the Ulster Division of the Royal Naval Reserve, and stayed on as a working naval vessel until 2011, almost a century after her launch. Restored and reopened as a museum in 2016, she sits a short walk from where Titanic sailed. During the Second World War the entire port served as a base for Atlantic convoy escorts, and German bombers came looking for it during the Belfast Blitz of April and May 1941. The shipyard was hit. The convoys kept sailing.

When Harland and Wolff began closing slipways in the 1980s, the harbour found itself with hundreds of acres of disused industrial land - all of it just across the water from Belfast city centre. The result, two decades later, is the Titanic Quarter: apartments where rivet shops used to be, a film studio where Game of Thrones was shot, the Catalyst Inc innovation campus, and the Titanic Belfast museum, which opened in 2012 on the hundredth anniversary of the disaster and looks from the outside like four iceberg-shaped prows pointing at the sky. The harbour still owns and develops the land, still describes itself as a trust port - independent of government, obliged to operate commercially, accountable to a board appointed through open public advertisement. It is a hybrid arrangement, neither private nor state, that has somehow allowed a Victorian dock to keep reinventing itself for two hundred years.