March 16, 2017

If there’s one thing people associate with St. Patrick’s Day–and by extension, Ireland itself–it’s the color green. And with good reason: the Emerald Isle is famous for its verdant landscapes, and there’s a bright green bar on its national flag.

But green wasn’t always synonymous with Irish pride. During the 16th century, experts believe, the national color was blue; when Henry VIII identified as King of Ireland, that was the color of his flag. (In fact, the Irish presidency is still represented by a blue flag with a harp.)

That started to change during the Great Irish Rebellion in the 17th century, during which displaced Catholic landowners and bishops rebelled against Protestant settlers and their English allies. One of the rebel leaders, Owen Roe O’Neill, used a green flag with a harp to represent his Catholic confederation. Although he was ultimately defeated, O’Neill’s flag helped turn the color green into a national “symbol of endurance,” says Timothy McMahon, vice president of the American Conference for Irish Studies.

The color popped up again during an effort in the 1790s to bring republican politics to Ireland, inspired by the American and French revolutions. One police report described the uniform of the Society of United Irishmen, a group that promoted this idea, as a dark green coat, green and white striped trousers, and a felt hat with a green cockade. Though the striped pants may have been a passing fad, the Irish love of green–buoyed by poems and ballads, most famously “The Wearing of the Green”–has endured ever since.

For more of these stories, visit time.com/history

This appears in the March 27, 2017 issue of TIME.

Write to Olivia B. Waxman at olivia.waxman@time.com.

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