Edward Cargill was the eighth child of William Cargill, the Scottish soldier and politician who had founded Dunedin as a Free Church of Scotland settlement in 1848. By the 1870s, the Cargill name carried weight throughout Otago. Edward chose a promontory along the southern coast for his family home, a site he called The Cliffs. He commissioned Petre and contracted builder Harry Lyders to construct it at a cost of 14,000 pounds -- a substantial sum for the era. What rose from the headland was not a castle in any medieval sense, but an Italianate mansion with a tower, loggias, and concrete roofs. It was one of only about ten buildings in New Zealand grand enough to earn the word 'castle,' the other in Otago being Larnach Castle on the nearby peninsula.

The most remarkable thing about Cargill's Castle is what it was made of. In 1877, reinforced concrete construction was still in its infancy worldwide. Petre and Lyders used several different types of reinforcement throughout the structure -- concrete roofs on the loggia and tower, concrete floors, concrete walls. The variety of techniques makes the building an early and significant example of the technology, not just in New Zealand but internationally. Petre would go on to become one of New Zealand's most celebrated architects, known for his bold use of concrete in major churches and public buildings. The Cliffs was where that ambition first took physical form, a testing ground perched above the ocean.

While sketching rooms and supervising construction, Petre fell in love with Edward's daughter Margaret. The courtship was anything but smooth. Petre was a staunch Catholic; the Cargills were equally staunch Presbyterians, descendants of a family that had helped establish Dunedin as a Scottish Protestant settlement. In a young colony where religious identity still shaped social boundaries, the match was deeply contentious. How long the impasse lasted is unclear, but the family eventually relented. On 1 March 1881, Francis and Margaret married in the villa's principal salon -- the very room Petre had designed for his client now serving as the setting for his own wedding. It remains one of the more romantic footnotes in New Zealand's architectural history.

In 1892, fire gutted the interior of the castle. Edward Cargill rebuilt what he could but lacked the resources to replace all the wooden furnishings destroyed in the blaze. He did manage to add a ballroom during the restoration -- a gesture of defiance, perhaps, against the damage. But the fire marked the beginning of a long decline. Over the decades that followed, the building deteriorated. Today only the concrete shell remains, its roofless walls standing on the promontory like the bones of some grand ambition. The ruins are surrounded by modern residential subdivisions, and there is no public access to the site. A few kilometres south, however, the family's other legacy endures: Tunnel Beach, reached through a steep tunnel carved into the 60-metre cliffs by the Cargill family, likely supervised by Petre himself.