A massive crowd gathered at City Hall in Philadelphia Thursday for a May Day rally and to see Vermont Sen. Bernie Sanders speak. The "For Workers, Not Billionaires" rally on the north side of City Hall drew a large crowd and shut down streets in the area.

The mass demonstrations occurred on a day that historically has been the province of a variety of causes. May 1 is “Loyalty Day” in the United States, first proclaimed during the administration of President Dwight D. Eisenhower in the 1950s at the peak of “Red Scare” and Cold War era.

Thursday’s rally and march comes amid economic uncertainty created by Trump’s on-again, off-again approach to tariffs — taxes on imported goods — which