It is not a castle keep, not a church, and its proportions are wrong for either. What it actually is, or rather what it was, is a smock windmill, a type of mill with a fixed base and a rotating cap that carries the sails, and at the time of its construction it was the largest of its kind in Europe.

The story begins in 1757, when Peter Roe purchased a small distillery on Thomas Street, establishing what would become George Roe and Company. The windmill provided the mechanical power to drive the distillery's operations, a practical solution on a city site without a reliable water source. Over the following century the business expanded dramatically. By 1887 the Thomas Street Distillery covered seventeen acres and had grown into the largest distillery in Europe, producing two million gallons of whiskey annually. Geo. Roe and Co. exported heavily to the United States, Canada, and Australia. The family's wealth was considerable enough that they funded the restoration of Christ Church Cathedral in the 1880s. The twentieth century, however, brought sustained difficulty to the Irish whiskey trade. Production at Thomas Street ceased by 1926, though large quantities of unsold stock remained in storage. The limited company dissolved in the mid-1940s, and in 1949 Guinness acquired the site.

The tower now sits within the Guinness St. James's Gate complex and is known as St. Patrick's Tower. Access to the surrounding area is possible through the Guinness Storehouse visitor attraction on Thomas Street, though the tower itself is not always accessible to the public as a standalone structure. It is worth walking along Thomas Street and the surrounding lanes to get a sense of the industrial scale of what once operated here. The tower's survival, while the distillery around it vanished entirely, gives it a slightly incongruous quality, a piece of machinery from one of Dublin's great industrial enterprises, now marooned inside the premises of its eventual successor.