Who Decided a Day Has 24 Hours?

There is no natural reason a day should have twenty-four hours. The Earth does not divide itself. Somebody chose that number, and the choice is older than almost every civilisation you have heard of. This is where twenty-four came from, why the hours were not even the same length for most of history, and what had to be invented before an hour could mean the same thing twice. Names, dates and places where the record has them. Where it does not, we say so. Who Signed It - every rule you followed today, somebody wrote.