Townsville existed because of trade. Founded in 1865 by John Melton Black on behalf of the Sydney merchant Robert Towns, the settlement lived and died by what moved across its wharves. The discovery of gold inland - at Cape River, Ravenswood, and the fabulously rich Charters Towers field - poured a fortune through the harbour from the late 1860s onward, and sugar from the surrounding plantations added to it. A customs house stood at the centre of all this, collecting the duties that funded the colony. The building Townsville had by the 1890s was the fourth on the job and plainly too small for a port handling this much money. The town had outgrown its own front desk.

The timing was deliberate. As the Australian colonies prepared to federate into a single nation on 1 January 1901, Queensland rushed to build and upgrade customs houses across the state - a parting investment before these buildings passed to the new Commonwealth. Townsville's was designed in 1899 by George Payne, a London-trained architect who had landed a temporary post in the Queensland Public Works Department after the depression of the 1890s wrecked his Sydney practice. Payne understood the tropics. He gave the building high ceilings for air to circulate and wide colonnaded verandahs to shade the rooms, dressing the whole in a confident Romanesque style. The tender of 26,642 pounds went to Crawford and Cameron of Brisbane, and the building rose in brick and stone on a plinth of granite quarried from Magnetic Island, just across the bay.

Completed in late 1902, the Customs House promptly met the north's other defining force: the weather. Cyclone Leonta struck in March 1903 and sent two chimneys crashing through the roof into an office below. The roof leaked, was re-clad, leaked again, and was rebuilt more than once over the decades, including after Cyclone Althea in 1971. Through it all the great Long Room - the public hall, modelled on British customs tradition - remained the heart of the place. During the Second World War the building bent to new purposes: the basement became an air-raid shelter with an exit onto Wickham Street, a mezzanine was thrown up inside the Long Room, and the Commonwealth's works department ran the construction of military facilities across north Queensland from these rooms.

For close to a century the Customs House did the job it was built for, serving the Australian Customs Service until the place finally passed out of Commonwealth hands. Careful restoration in 1983 won a conservation award, and a federal grant in 1992 paid to repair the sandstone, masonry, and roof. Today the two-storey, L-shaped building still commands its corner of The Strand at the foot of Melton Hill, its semicircular entrance and dome anchoring a streetscape of grand survivors - the old Queen's Hotel, the former Bank of New South Wales, Tattersalls Hotel. It earned its place on the Queensland Heritage Register in 2005. To stand before it is to read, in brick and sandstone, the precise moment a frontier port decided it had become a city.