Which European stock exchange suffered the largest one-day percentage loss during the 1873 financial crash?

The Vienna Stock Exchange suffered the largest one-day percentage loss during the 1873 financial crash.

The Vienna market collapsed on May 9, 1873, a day remembered as Black Friday or Gründerkrach. Share prices had risen rapidly during an investment boom after the Austro-Hungarian Compromise of 1867, and speculation was encouraged by easy credit and the creation of many companies. When confidence broke, investors rushed to sell.

The Vienna crash helped trigger the Panic of 1873, an international financial crisis. The shock spread through central European banking and securities markets, then affected economies including Germany and the United States. In the United States, the failure of Jay Cooke & Company in September 1873 helped turn financial stress into a major panic.

The term Black Friday can refer to several unrelated events, including the 1869 U.S. gold panic and the 1929 market crash week. In the context of the Panic of 1873, it specifically identifies the Vienna market collapse of May 9.