On October 12, 1820, Florence Nightingale was born in Florence, Italy — she was named for the city — into a wealthy English family that expected her to marry and manage a household. She was called to nursing as a vocation, which her family resisted for years. She eventually won out, studied nursing in Germany, and became superintendent of a hospital for governesses in London.

When Britain entered the Crimean War in 1854, newspaper reports from the front described catastrophic conditions in military hospitals — soldiers dying of infection and disease at rates that dwarfed combat casualties. The Secretary of War, Sidney Herbert, was a friend of Nightingale's family. He asked her to take a party of nurses to the front. She arrived at the Scutari barracks hospital in November 1854 with thirty-eight nurses.

She found a hospital without basic sanitation — open sewers, no ventilation, inadequate water, food rotting in the wards. She secured supplies, organized the wards, and implemented sanitation protocols. The mortality rate dropped from over 40 percent to just over 2 percent during the winter of 1854–55. She kept meticulous statistical records of causes of death and used them to demonstrate that infection and disease — preventable through sanitation — were killing far more soldiers than enemy fire.

She returned to England and spent the next forty years of her life largely bedridden, conducting the most consequential public health reform campaign in British history through letters, reports, and statistical analysis. She invented the polar area diagram — the "rose diagram" — to communicate mortality data visually. She reformed military hospitals, then civilian hospitals, then worked on sanitation in India without ever going there.

She received the Order of Merit in 1907. She was the first woman to receive it.