Associated Press

On July 31, 1777, the 19-year-old Marquis de Lafayette received a commission as major general in the Continental Army by the Second Continental Congress.

In 1919, Germany’s Weimar Constitution was adopted by the republic’s National Assembly.

In 1957, the Distant Early Warning Line, a system of radar stations designed to detect Soviet bombers approaching North America, went into operation.

In 1964, the U.S. lunar probe Ranger 7 took the first close-up images of the moon’s surface.

In 2012, at the Summer Olympics in London, swimmer Michael Phelps won his 19th Olympic medal, becoming the most decorated Olympian of all time.

In 2020, a federal appeals court overturned the death sentence of Dzhokhar Tsarnaev in the 2013 Boston Marathon bombing, saying the judge didn’t adequately screen jurors.