Locals still call it the Ring of Mahon, the older name for the peninsula. The Irish rinn means a point of land, and Mahon is the anglicised spelling of the Gaelic Machain - a reference to the O'Mahony clan who controlled this stretch of the harbour in medieval times. In 1839 the Cork antiquarian John Windele included the etymology in his Historical and Descriptive Notices of the City of Cork, the kind of book that fixed Irish place-names in print just as Victorian Cork was beginning to forget them. Ringmahon Castle appears on seventeenth-century maps of the peninsula, though the exact date of its building was already lost by then. The Crawford and Chatterton families held it before the Murphys took the lease at the start of the nineteenth century. In 1769, James Murphy of the Murphy's Brewery family was born here and would later build Ringmahon House on the site. The house still stands, having sheltered, among others, the businessman Ben Dunne of Dunnes Stores.

Lough Mahon is not a lake but a tidal expanse - twelve square kilometres of upper Cork Harbour, reaching from the Mahon peninsula southward to Passage West and inland to take in the estuary of the Douglas River. At high tide it is a great sheet of brackish water with the southern suburbs of Cork strung along its rim: Mahon, Blackrock, Douglas, Rochestown. At low tide it becomes something else entirely - mudflats the colour of milk chocolate, ribbed and channeled, busy with curlews, redshanks, and migrating waders working the exposed sediment for invertebrates. Birdwatchers come for the autumn passage, when the flats fill with shorebirds taking their last meals before continuing south. The peninsula's eastern shore looks across the lough toward Little Island and the petrochemical jetties at Marino Point. The view is industrial and lovely at once.

Just over the boundary in Blackrock, the ruined sixteenth-century Dundanion Castle stands quietly above the harbour. From this point, according to tradition, William Penn sailed for America in 1682 - the founder of Pennsylvania and the namesake of the American state, taking his Quaker convictions and a royal land grant across the Atlantic. He had a long association with Cork. His father Admiral Penn had been granted lands at nearby Macroom and then at Shanagarry, where William Penn lived after he became a Quaker in his twenties. Whether he literally departed from Dundanion or simply from Cork Harbour is one of those historical details that has become tradition through repetition. The harbour was certainly his point of embarkation. The story of an empire-changing colonial venture beginning at a Cork ruin sits oddly beside the Mahon Point cinema and the lunchtime crowds at the City Gate offices, but Cork is full of these juxtapositions.

Mahon's late-twentieth-century transformation happened fast. The N40 ring road came through along the peninsula's eastern and southern edges, plunging into the Jack Lynch Tunnel under the Lee. Housing estates filled the old farmland. Schools followed - Nagle Community College in 1981, Scoil na Croise Naofa in 1984, the Irish-medium Gaelscoil Mhachan in 1986 - on streets named for Cork's twin city Rennes in France. Mahon Golf Club opened in 1980 on Skehard Road, designed by the great Irish course architect Eddie Hackett, and was the first purpose-built municipal golf course in Ireland. Then in the early 2000s came Mahon Point Shopping Centre, sixty stores and a thirteen-screen cinema, the largest shopping destination in Cork and the second-largest in the province of Munster. The City Gate office complex went up beside it, drawing the Central Statistics Office, PM Group, the timeshare company RCI, and a cluster of medical practices. RedFM, a Cork radio station, broadcasts twice a week from a pod inside the shopping centre - an oddly literal version of being on the high street.

Mahon punches above its weight in Cork sporting life. St Michael's GAA Club and Ballinure GAA Club represent the area in Gaelic football and hurling. Ringmahon Rangers, the local football club, has produced an unusual number of professional players, including Alan Browne, born in 1995, who plays in the English Championship for Preston North End. Wayne Sherlock, the All-Ireland hurler with three Cork titles and an All Star award, grew up here. The Olympic walker Robert Heffernan, world champion at 50 kilometres in Moscow in 2013, lives in Mahon with his wife Marian, also an Olympic runner. Gary O'Sullivan, the former Irish middleweight boxing champion, is another Mahon name. For a suburb that did not really exist in its modern form until the 1980s, the place has produced an extraordinary roll-call of athletes - the kind of statistic that suggests good clubs and stubborn coaches more than it suggests destiny.