Schaffhausen had fought alongside the Eidgenossen during…
August 1501 CE
Schaffhausen had fought alongside the Eidgenossen during the Swabian War, and thus its acceptance into the Confederacy is a mere formality.
The city had been an imperial city since 1415 and an associate state of the Confederacy since 1454 through a twenty-five-year contract that had been renewed in 1479.
On August 10, 1501, it becomes the twelfth member of the Confederacy.