"It posed a major risk to motorists," said Staff Sgt. Jan Idzenga.
"Travelling at highway speeds, if you would strike a horse of that size and mass, it would cause substantial damage -- and who knows what else would have happened."
Port Colborne Fire Chief Tom Cartwright was driving into the city around 10 a.m. when he spotted the horses at the side of the road.
"They were just walking along, eating grass," he said.
Cartwright parked his truck, equipped with flashing emergency lights, along the side of the highway to try to block the animals from venturing onto the road.
"They ended up coming right onto the highway and walked to the centre median and turned around and walked back."
A number of motorists also stopped their cars, and the group tried to herd the horses out of harm's way.
"They obviously didn't want the animals to get hurt, and we can all imagine the catastrophic events that could have occurred if someone were to hit one," Idzenga said.
The animals eventually walked onto a grassy hill on the east side of the highway.
The Niagara Falls Humane Society subsequently located the horses near a cemetery.
Humane society manager Jay Desroches said it appears the horses escaped by slipping through a fallen section of fencing on a property.
The horses' owner was able to coax the animals with food and load them into the back of a trailer.
The owner did not want to speak to the media.