At the close of WWI, an estimated 50 million people died from the Spanish Flu. Masks were the uninfected’s main line of defense.

The Spanish flu pandemic of 1918, the deadliest in history, infected an estimated 500 million people worldwide—about one-third of the planet’s population—and killed an estimated 20 million to 50 million victims, including some 675,000 Americans.

The 1918 flu was first observed in Europe, the United States and parts of Asia before swiftly spreading around the world. At the time, there were no effective drugs or vaccines to treat this killer flu strain. Citizens were ordered to wear masks, schools, theaters and businesses were shuttered and bodies piled up in makeshift morgues before the virus ended its deadly global march.

Why “Spanish”? According to Mashable, to read the newspapers of 1918, Spain was hit particularly hard by the virus. On the contrary: 1918 was the last year of World War I and, in an attempt to maintain morale, the United States, Britain, France and Germany suppressed newspaper reports of the illness. Neutral Spain, with no war morale to maintain, did not censor its newspapers; so, to the rest of the world, the flu appeared particularly nasty there.