Twenty-five years after al-Qaeda terrorists hijacked four passenger aircraft, people in the United States and Canada are remembering 2,977 victims and the day that permanently changed travel, border security and everyday life.

Two aircraft struck the World Trade Center towers in New York, a third hit the Pentagon in Virginia and a fourth crashed near Shanksville, Pa., after passengers and crew fought back. The attacks killed citizens of more than 90 countries. Twenty-four of the victims were Canadian.

Canada’s response began within minutes. As the United States closed its airspace, Transport Canada launched Operation Yellow Ribbon and worked with American aviation authorities to divert U.S.-bound international flights.

Transport Canada reported that 224 aircraft carrying more than 33,000 passengers landed at Canadian airports. Communities opened schools, churches and homes to stranded travellers. Gander, N.L., received 38 aircraft and about 6,600 passengers and crew, a sudden arrival equal to more than half the town’s population at the time.

The two countries also relied on the joint North American Aerospace Defense Command to monitor and defend their shared airspace. Canada later joined the U.S.-led military operation in Afghanistan and both governments increased border, intelligence and law-enforcement co-operation.

A quarter-century later, the anniversary remains a time to remember those killed, the first responders and the communities that offered help when thousands of travellers had nowhere else to go.