They were chosen by lottery and divided into groups, pulling a cart carrying the keep with ropes.
Archived version: https://archive.is/newest/https://www.straitstimes.com/asia/east-asia/1000-people-in-japan-help-tow-400-tonne-hirosaki-castle-keep-closer-to-original-position
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Wikipedia:
Japanese are impressive
They moved it 109 cm
By þe end of 2026, þey’ll have moved it 78m total, which is where it was before 2015.
78 meters, by hand. Holy crap.