Pesthouses, as they were known, were buildings used to isolate those suspected of carrying infectious disease, functioning as a kind of enforced quarantine station at a remove from the general population. The practice of placing them on islands or at the margins of settlements was deliberate: distance was the only reliable medicine available.

According to John de Courcy's 1996 study of the Liffey, pesthouses were constructed on Clontarf Island, the earlier name for what is today Bull Island, in 1666. The timing is suggestive. The Great Plague had devastated London the previous year, and anxiety about contagion spreading through ports and coastal towns was running high across these islands. Dublin, as a busy harbour city with regular traffic from England, had good reason to establish a point of interception. The island location made practical sense: those arriving by sea could be held at a distance before being permitted into the city proper. Beyond that single reference in de Courcy, little else is recorded about the buildings themselves, who administered them, or how long they remained in use. Their precise location on the island has not been established.

Bull Island today is a nature reserve, best known for its sand dunes, bird life, and the long curved strand that faces the Irish Sea. It is accessible via a wooden bridge from the Clontarf Road, or by the causeway road that leads to the Royal Dublin Golf Club. There is nothing visible above ground to mark where the pesthouses stood, and the island's landscape has changed considerably over the centuries as sand accumulated and the shoreline shifted. Anyone walking the island with this history in mind is essentially reading a blank page, which is in its own way instructive: the buildings served their purpose at the edge of the city and then disappeared, leaving almost no trace except a line or two in the historical record.