A cannonball fired by the British during the Battle of the Plains of Abraham in 1759 has been unearthed at a building site in Old Quebec.

The rusted, 90-kilogram projectile was unearthed during excavation work last week at the corner of Hamel and Couillard streets and still contained a charge and gunpowder.

The work crew that found the ball picked it up and gathered around it for photographs, unaware that it was still potentially explosive.

Municipal authorities were contacted, and archeologist Serge Rouleau was called in.

Rouleau brought the cannonball back to his home, and noticed it still contained a charge.

A team of army munitions technicians was dispatched from CFB Valcartier to collect the ball and neutralize it.

"With time, humidity got into its interior and reduced its potential for exploding, but there's still a danger," said Master Warrant Officer Sylvain Trudel, a senior munitions technician.

The cannonball is from Britain and was fired at Quebec City from Lévis, across the St. Lawrence River. (Facebook/Lafontaine Inc) Trudel said such balls were meant to set fire to the buildings they penetrated.

"The ball would break and the powder would ignite, setting fire to the building."

Trudel's team removed the cannonball to a safe site, where it will either be rendered harmless or destroyed if there's no other choice.

"Old munitions like this are hard to predict," Trudel said. "You never know to what point the chemicals inside have degraded."

Master Warrant Officer Sylvain Trudel points to the hole in the cannonball where the fuse was placed. (Marie France Poulin/CFB Valcartier) If it can be saved, the relic will be sent to a museum for display.

At the Battle of the Plains of Abraham in 1759, British forces defeated the French and seized control of Quebec City, setting the stage for their eventual conquest of Canada.

The brief battle cost the lives of the British General James Wolfe and the French commander, Gen. Louis-Joseph, Marquis de Montcalm.

It's believed the ball was fired at Quebec City from Lévis, across the St. Lawrence River.