1. On May 21, 1729, the city of Baltimore was founded. Originally called "Town of Baltimore," it was named after the Irish barony of Baltimore and established as a port of entry for tobacco trade.

2. On May 21, 1833, the first major riot against the abolition of slavery in Maryland occurred in Baltimore. Known as the "Prigg v. Pennsylvania" case, it involved a man from Pennsylvania who was arrested while trying to capture a fugitive slave in Maryland. The case stirred up tensions between northern abolitionists and southern slaveholders.

3. On May 21, 1894, the first electric trolley car service in Maryland began operating in Baltimore. The service was an instant success, providing a faster, cheaper transportation option for the growing city.

4. On May 21, 1927, Charles Lindbergh landed his plane at the old Logan Field in Baltimore on his historic cross-country tour. He was greeted by a huge crowd of admirers and became an instant celebrity.

5. On May 21, 1932, the Maryland state insect, the Baltimore Checkerspot butterfly, was designated as such by the state legislature. The butterfly is native to the region and is recognizable for its striking orange and black markings.