My wonder is the fortified Cité de Carcassonne, the origins of which can be traced back to 3500 BC.

Clive Sayer
Clive Sayer

As a quantity surveyor, I am particularly struck by how an ancient city could have been restored from dilapidation to such a magnificent monument – but in a style and using materials more typical of northern France than its Mediterranean environs. The architect Eugène Viollet-le-Duc was commissioned to complete the renovation in 1849 and made the error of using slates and restoring some roofs as pointed cones instead of following the local practice of constructing flat roofs with low slopes. This oversight initially caused uproar (as it would today!) but, as with many architectural peculiarities, the restored building soon became a much lauded work of genius and still attracts huge numbers of tourists every year.

My blunder is much more current: I noticed that a budding entrepreneur had been quick to spot the construction potential of recent weather conditions and put up for sale an igloo in Blackheath, south-east London. On the face of it, it has the elements of an attractive business opportunity: no carbon footprint, freely available construction material pre-delivered to site, a young and enthusiastic workforce and no onward chain. But there are disadvantages. The UK is an unreliable source of materials for further schemes and repair work, the labour force is extremely seasonal (likely to be otherwise employed at school) and current global warming trends suggest this may be a one-off business venture …

Cité de Carcassonne

Like the roman 

Over the past 5,000 years, forces including the Romans and Occitan Cathars have used the fortress at Carcassonne as a strategic stronghold. It fell into disrepair under Napolean’s rule and was saved from demolition only by fierce campaigning from the town’s mayor Jean-Pierre Cros-Mayrevieille. In 1849, architect Eugène Viollet-le-Duc was commissioned to lead the renovation. The Cité became a Unesco World Heritage Site in 1997.

Igloo in Blackheath, south-east London

Like the snowman 

The “Blackheath Igloo” sold for £9.30 on eBay in February. The anonymous seller marketed the property as a “beautiful open-plan eco-apartment” that uses “original materials” and “state-of-the-art natural ventilation”.