NEW YORK, NY.- Early last year, archaeologists discovered five round objects while working near trails at the Minute Man National Historical Park in Concord, Massachusetts. The spheres ranged from as small as a pea to about the size of a marble and were scattered in the dirt near the site of a Revolutionary War battlefield.

They were musket balls used at the outset of the American Revolution, the National Park Service said in July. The ammunition had gone undetected for centuries near the North Bridge, where colonist militias fired at British soldiers on April 19, 1775, in a skirmish immortalized in the poem “Concord Hymn” by Ralph Waldo Emerson as “the shot heard round the world.”

“At the North Bridge site itself, this is the first time the National Park Service discovered something related to the fighting that day,” said Jarrad Fuoss, a park ranger and weapon historian.

Artifacts of history can be discovered through the careful work of archaeological research, but will sometimes surface by accident. Hobbyists, treasure seekers, collectors or scientists scan the land where critical events unfolded, trying to outsmart years of change wrought by weather and development.

The musket ball findings came as archaeologists surveyed the park to ensure that a $27.4 million maintenance project, preparing for next year’s 250th anniversary of the revolution, would not disturb any cultural resources, Fuoss said.

“It is a reminder of how fragile the landscape can be,” said David Wood, curator of the Concord Museum, who was at the site when the musket balls were discovered. “You don’t always think of the fact they were still there, even though the fields had regularly been plowed for two centuries.

“The slightest thing could have swept them away, and then you would never know.”

The town of Concord, which is about 20 miles northwest of Boston, contains both the remnants of the war and the houses of many of its participants.

Many revolutionary-era findings are displayed in the Concord Museum. In the 19th century, Henry David Thoreau, the naturalist and philosopher, found musket balls near the North Bridge, where provincial militias from Concord and nearby towns had fired across the span at the British troops trying to block their advance.

In 1934, Benjamin Smith, a Concord man and a collector of Native American objects, was attracted to a reflection in the dew of a nearby field where the provincial militias of Massachusetts were known to have gathered before confronting the British.

There, he discovered flints, which are used to create the spark to ignite gunpowder. “Gun flints seemed to be everywhere and they stood out against the dark, wet ground like glittering jewels,” Smith said in a speech in 1961.

Wood said that physical context was as important as each archaeological find. The discarded flints, in two rows about 30 feet apart, gave a glimpse into the moments when the men swapped them out as they mustered for a fight.

“Within minutes, they marched down to the bridge,” he said. “It is one of the most extraordinarily audacious things to do, in sight of the British regulars.

“This is the virtue of archaeology, when it tells us things no other record reveals.”

The analysis of the musket balls at the North Bridge provided another snapshot of the fight that day, even though it lasted just a few minutes. Farmers, hunters and other men took up weapons, including personal hunting muskets. So did young fighters known as Minutemen, who were ready at a moment’s notice.

The musket balls that were found ranged in caliber from .40 to .70 and show marks of rubbing, scrapes and gunpowder, indicating they were fired rather than dropped. None of them appeared to have met their mark: There were no signs of deformity from impact, Fuoss said.

The musket balls are made of lead and were probably produced in the months leading up to the fight at the North Bridge, Fuoss said. “Houses were filled with stockpiles produced by the people of Concord,” he said.

Three British soldiers were shot dead, while two Minutemen from the Acton Minute company were killed, Wood said.

For Wood, the events of that day were made tangible by the finding of the musket balls, despite the passage of time. “The interval evaporates when you stand there,” he said. “It just disappears.”

This article originally appeared in The New York Times.