September 1929 marked the peak of the Dow Jones Industrial Average before the Wall Street crash.
The Dow reached its pre-crash closing high on September 3, 1929, at about 381. The market then became increasingly unstable. A major decline in late October included Black Thursday on October 24, Black Monday on October 28, and Black Tuesday on October 29.
The September peak is important because it shows that the crash did not begin at the month’s end. Speculative enthusiasm had pushed stock prices sharply higher during the 1920s, while many investors bought shares on margin. When prices weakened, forced selling and collapsing confidence intensified the fall.
The Dow continued dropping long after October 1929. It eventually reached a low in July 1932, losing roughly 89 percent from its 1929 peak. Thus, September identifies the high-water mark, not the end of the entire bear market.