21 August in history.

1883

From a tornado, a hospital. After a tornado struck Rochester, Minnesota, Dr William Mayo and his sons cared for the injured with local nuns. Their work grew into the Mayo Clinic.

Wikipedia: Mayo Clinic

Photo: Mayo Clinic / Wikimedia Commons (Public domain)

More from 21 August

1. 

   1789

   Italy's colours

   The green, white and red that became Italy's flag first appeared together on a cockade in Genoa.

   Wikipedia: Flag of Italy

   Photo: See below. / Wikimedia Commons (Public domain)

2. 

   1862

   Vienna's first public park

   Vienna opened the Stadtpark, the city's first public park.

   Wikipedia: Stadtpark, Vienna

   Photo: KF at English Wikipedia / Wikimedia Commons (Public domain)

3. 

   1888

   An adding machine

   William Seward Burroughs patented a practical adding machine, the start of the Burroughs company.

   Wikipedia: William Seward Burroughs I

   Photo: Unknown author / Wikimedia Commons (Public domain)

4. 

   2017

   The Great American Eclipse

   A total solar eclipse crossed the United States from coast to coast, watched by millions.

   Wikipedia: Solar eclipse of August 21, 2017

   Photo: Michael S Adler / Wikimedia Commons (CC BY-SA 4.0)

Moments chosen for discovery, creativity and courage. Each one links to a source where you can read more; photos are credited to their owners.