The stock market rally that kicked off more than nine years ago during the financial crisis is now arguably the longest on record in the United States.*

[*By one measure. Read about the caveats here.]

The Standard & Poor’s 500-stock index has marched steadily higher for 3,453 days. Since bottoming out on March 9, 2009, it is up more than 320 percent.

Investors have enjoyed 11 bull markets — defined as a period without a pullback of 20 percent or more — since the end of World War II. Usually driven by a strengthening economy that fuels corporate profits, bull markets often end in recession after the Federal Reserve begins to raise rates to slow rising prices and cool the economy.