We built this archive in 2024, during the year Cluj-Napoca hosted the Eurocities Annual Conference. Two hundred and fourteen city profiles, each one naming the person who ran the city. Then we left it alone.

This month we checked every one of those names. Of the 206 cities in the archive, 84 named the wrong person. Eighty-one were still right. For 44 we could not establish who holds the office from a source we were willing to cite, so those profiles now name nobody.

The mistake was not writing it. It was not revisiting it.

Almost none of those 84 were wrong when they were published. They went stale, and they went stale in clusters, because local government in Europe does not turn over gradually — it turns over on election days.

France went to the polls on 15 March 2026, with a second round on 22 March. That single weekend accounts for nine of our errors on its own. Anne Hidalgo had run Paris since 2014 and our profile said so; Emmanuel Grégoire won the city for the Socialists and the sentence became false overnight. In Bordeaux, Thomas Cazenave beat the incumbent Pierre Hurmic. Nice, Grenoble, Angers, Amiens, Pau, Saint-Étienne and Strasbourg all changed hands in the same round.

North Rhine-Westphalia voted on 14 September 2025, with run-offs on the 28th. The mayors elected there took office on 1 November, and six of our German profiles — Cologne, Bonn, Bochum, Dortmund, Hagen and Münster — were wrong from that date.

Then there are the individual cases that no calendar predicts. Bart De Wever was Mayor of Antwerp when we wrote about it; he has been Belgium’s prime minister since February 2025, and Els van Doesburg has the city. Ekrem İmamoğlu was Mayor of Istanbul. Kostas Bakoyannis lost Athens in 2023, a year before we published, which makes that one an error at the time of writing rather than a stale fact.

What we changed about how we do it

The fix was not to correct 84 names by hand. It was to stop storing them as prose.

Every city in the archive is now resolved to a stable identifier — its Wikidata Q-number — and the office-holder is read from two independent places: English Wikipedia’s infobox and Wikidata’s P6 statement. A name is published only where at least one of them carries it, and every profile shows which sources were used and the month they were read.

Doing this taught us not to trust a single machine-readable source, including the one everybody reaches for first. Searching Wikidata by name returned the governors of the Kharkiv, Lviv and Poltava oblasts in place of the mayors of those cities. It still listed Chiara Appendino for Turin and Lars Weiss for Copenhagen years after both had left, because a P6 statement stays open until somebody closes it. In every disagreement we checked by hand, Wikipedia’s infobox was the one that was right. So Wikipedia leads and Wikidata corroborates, rather than the other way round.

The part worth saying out loud

Forty per cent is not a rounding error, and the people involved are named public officials. A profile that tells a reader Anne Hidalgo runs Paris is not a small inaccuracy — it is the site being confidently wrong about the single fact a reader is most likely to check.

An archive is a promise that what you wrote is still what you would write. We were not keeping it. We are now, and the check re-runs against both sources rather than against our memory.