Founded: how many castles are there?

A Hacker News thread took apart a map of “the world’s 2,400 castles” today. The coverage complaints were loud — Saxony showing nine structures against a literature that counts hundreds, France showing about a hundred against a folkloric forty-five thousand. But the sharper problem was quieter: the map published a single integer for a contested term.

Canonical Castles is the answer we thought that deserved.

It never records that something is a castle. It records a verdict against each of six named definitions — fortified residence, enclosure fortification, state fortification, palatial seat, revival and folly, and popularly a castle — each with a cited authority, an explicit criterion, and its own closure rule. Three of those bands can in principle be counted to completion against national registers. Three cannot, and never will. The site says which is which everywhere it prints a number, and it publishes a count per band rather than a total across them.

Ireland settles the argument on its own. The state’s Sites and Monuments Record answers “how many castles?” with 129, 4,552 or 31,431 — same database, same day, depending only on which class filter you accept.

Three things we found while building it:

• Only 19.5% of OpenStreetMap objects carrying a castle_type are tagged defensive. The rest are stately homes, manors and palaces.
• “France has 45,000 châteaux” is folklore. No primary source, no stated method, and it circulates as 20,000, 30,000, 40,000 and 45,000 simultaneously — the signature of a meme, not a statistic. The register supports about 6,286, and even that depends on which of four defensible tokenisations you use.
• Northern Ireland’s register has a castle type. Querying it returns 4. Its castles are filed under FORTIFICATION.

The seed dataset is thirteen records, collected by hand from a console session — no research agent has run against this repo yet, and the provenance page says so rather than implying otherwise. Thirteen records is a seed, not a survey, and the coverage grid states cell by cell what has been examined, what has not, and which register would close each open one.

A Bussetech Software Studio project.