After witnessing the British bombardment of Fort McHenry during the Battle of Baltimore on the night of September 13, 1814, Francis Scott Key was moved to immortalize the scene in what became the U.S. national anthem: "the rockets' red glare, the bombs bursting in air…"

Many cite Key's depiction of battle as a driving force behind the American tradition of setting off fireworks each Independence Day. Now, firework technology has evolved to give a wide range of possible colors, sounds and designs.

So how similar are firework displays to the original munitions that inspired them?

Harry Porfert, a historian with more than 30 years of war reenactment experience, says the most common types of explosions seen during the Revolutionary War and the War of 1812 weren't in the air. "Mostly you'll be seeing the musketry or the discharge of the cannons," he says.

The wars were hardly short on explosives. Heavy artillery during the late 18th and early 19th centuries featured powerful weapons capable of turning the tide of battle. During the Siege of Boston from 1775 to 1776, American mortars, short, heavy cannons designed to fire explosive rounds, rained rounds down on British troops fortified in the city, eventually causing the British to withdraw.

Era mortars bore a similarity to witches' cauldrons and were capable of shooting explosive projectiles up to 13 inches in caliber across distances of hundreds of meters. While crude by modern standards, the smoke and explosions would have been both devastating and psychologically intimidating. Still, most explosions occurred after the projectile landed, and pale in explosive size compared to modern fireworks.

"If you're in a siege, lots of mortars would have been brought in," Porfert says. "You would have been able to see the explosions inside the British fortifications."

These types of munitions go widely unmentioned in popular culture. "One of the biggest fallacies when you watch any movie is that cannonballs explode," Porfert says. "That was more the exception than the rule for regular field guns." Instead, the cannonballs just travel and strike with great impact.

So what did Key see over Fort McHenry that fateful night in 1814?

At the time, Key was held on a British ship in the harbor, having arrived there to negotiate the release of American prisoners. Because he was aware of the size of the British fleet, he was not permitted to return to the American lines, forcing him to watch the bombardment of Fort McHenry from afar.

“From the ship he would have seen direct fire from broad guns, which were not explosive,” Porfert says. These were the cannons on the sides of the British ships. There were also British mortar schooners, firing ten-inch explosive rounds at the American position. He would have been able to see the mortar fuses shooting through the sky and the shells as they exploded—surely many exploded in the air before reaching their mark.

Another visually stunning type of weapon was in use that night: a “carcass” round. An explosive mortar shell wrapped with incendiary material, this round was fully engulfed in flame after being fired, streaking through the air before exploding.

“This whole thing was on fire all the way through the sky,” Porfert says. “There was definitely quite a bit of fire and smoke in the air over the fort."

Although somewhat exaggerated from Key’s original description, modern fireworks displays indeed bear similarities to antiquated munitions used in battles over U.S. soil and are an important part of culture worldwide.

“Fireworks are still using black power, which throws a lot of sparks and smoke, unlike modern smokeless powders,” Porfert says. “When the Chinese made them, they were designed for big aerial displays.”

And that’s exactly what they’re used for: this year, Macy’s Fourth of July Fireworks in New York City will consist of more than 40,000 fireworks synchronized to a 25-minute musical score—and the whole thing is directed by Usher.