The New York Stock Exchange event on October 24, 1929, that marked the start of the Wall Street Crash was Black Thursday.
On that day, panic selling caused the market to open sharply lower. A group of major bankers, including Richard Whitney, attempted to restore confidence by buying shares, temporarily slowing the decline. The intervention did not solve the underlying problems in the market.
Selling resumed during the following sessions. October 28 became known as Black Monday, and October 29 became Black Tuesday. The crash continued beyond those famous dates, with the Dow eventually reaching its low in July 1932.
The crash did not single-handedly cause the Great Depression, but it became one of its defining financial events. Falling share prices damaged confidence, reduced wealth, and intensified pressures already affecting banks, businesses, consumers, and international trade.