In the 1929 Wall Street Crash, the Dow Jones Industrial Average plunged 12.8% on Black Monday, October 28, 1929.
The fall came after a sharp decline on Black Thursday, October 24. Selling intensified as investors and brokers struggled to meet margin calls on highly leveraged share purchases. The next day, Black Tuesday, October 29, brought another catastrophic wave of selling.
Black Monday is sometimes confused with Black Tuesday because both days were exceptional. Black Tuesday produced a larger point loss, while Black Monday recorded the larger percentage fall. Together, the two sessions became the most famous opening phase of the Wall Street Crash.
The crash did not by itself cause every aspect of the Great Depression, but it badly damaged confidence and contributed to a wider contraction in investment, banking, trade, and employment.