The Liffey gave Dublin its name twice over. The English version comes from Dubh Linn - dark pool - the tidal basin where the small River Poddle once spilled into the Liffey near the present site of Dublin Castle. The Irish name, Baile Átha Cliath, refers to the ford of hurdle reeds the Liffey could be crossed at when it was shallow enough. Two names for two facts of the same river: the deep place where Viking longships could anchor, and the shallow place where everyone else could wade across. Both points sit within a few hundred metres of one another, both shaped Dublin's earliest streets, and both have since been built over. The Poddle now runs in a culvert beneath the city, surfacing only to discharge into the Liffey through a stone arch you can see at low tide near the Civic Offices.

Read the bridges from west to east and you read four centuries of Dublin politics. Mellows Bridge, built in 1764 on the wreckage of an older bridge swept away by floods, is the oldest still standing. The Ha'penny Bridge, a delicate cast-iron arch from 1816, charged a halfpenny toll until 1919 and gave the city its most photographed crossing. O'Connell Bridge is famously almost as wide as it is long. Then the twenty-first century brought the architects in: the James Joyce Bridge in 2003 and the harp-shaped Samuel Beckett Bridge in 2009, both designed by Santiago Calatrava, both controversial, both now beloved. The Rosie Hackett Bridge, named for the trade unionist and 1916 veteran, opened in 2014 and was the first Liffey bridge named for a woman since Sarah Bridge in 1792. Each addition shifted the city's centre of gravity a little further east, towards the old docklands now reborn as the Silicon Docks.

About sixty percent of the Liffey's flow is pulled out before it reaches the sea, abstracted at Poulaphouca and Leixlip to supply drinking water and industry, then returned through wastewater plants further downstream. Three ESB hydroelectric stations sit on the river - at Poulaphouca, Golden Falls, and Leixlip - holding back reservoirs that drowned what were once dramatic waterfalls. The Guinness brewery, despite the persistent myth, does not brew with Liffey water; St James's Gate draws from a pipeline that runs down from the Wicklow Mountains. Above Dublin, rowing clubs share the Chapelizod stretch with the Garda. The Liffey Descent canoe race has run every September since 1960, twenty-seven kilometres from Straffan to Islandbridge. And every late August the Liffey Swim sends competitors from Watling Bridge down to the Custom House, hundreds of swimmers in dark green water turning the quays into bleachers.

Walk east along the north quays from Heuston Station and the names change every hundred metres: Wolfe Tone, Sarsfield, Ellis, Arran, Inns, Ormond Upper, Ormond Lower, Bachelors Walk, Eden, Custom House, North Wall. The south side answers with Victoria, Usher's Island, Merchants, Wood, Essex, Wellington, Crampton, Aston, Burgh, George's, City, Sir John Rogerson's. Each quay was once a working dock; each marks a phase of mercantile Dublin. Usher's Island, on the south bank, is where Joyce set 'The Dead,' the closing story of Dubliners, in a house his great-aunts actually lived in. Wood Quay is where Wood Quay was - until Dublin City Council built its offices on top of the largest Viking-Age excavation in Europe, despite a march of twenty thousand people in 1978 begging them not to. The river remembers; the city occasionally does.

In Finnegans Wake, the river is a woman who is also Ireland who is also the protagonist's wife who is also history itself. Joyce wrote her in seventeen years of voluntary exile, working in Paris and Trieste while remembering the exact curve of the Liffey at every bridge. The 'Anna Livia Plurabelle' chapter - washerwomen on opposite banks gossiping as the river broadens towards night - is the most musical thing in the book and the most beloved. A 1988 statue of Anna Livia, a reclining bronze woman pouring water from her hands, was installed in O'Connell Street and promptly nicknamed 'the floozie in the jacuzzi.' She was moved in 2001 to make way for the Spire. She now reclines in the Croppies Acre Memorial Park near Heuston, less famous than her river but still there, still pouring.