History
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The decisions, accidents and people that shaped now.
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How a 9th-century scholar cracked secret codes by counting letters
For roughly nine centuries after Julius Caesar, swapping each letter for another was a perfectly good way to keep a secret. Then, in 9th-century Baghdad, the…
Why October 1582 lost ten days: a calendar year 11 minutes too long
In 1582, Thursday 4 October was followed by Friday 15 October. Ten dates were simply deleted across Catholic Europe. The reason was an error of about 11…