A look at previous security breaches on Parliament Hill

WATCH: In the aftermath of the Ottawa shooting, there are lots of questions about how a gunman got so close to politicians. Chief Political Correspondent Tom Clark discusses.

TORONTO — The nation’s capital is on high alert Wednesday following a shooting at the National War Memorial and reports of shots fired inside the Centre Block of Parliament Hill.

Security on Parliament Hill, which is mostly open to the public, was significantly boosted in 2009 after 20 Greenpeace activists managed to scale two of the buildings and unfurl banners protesting Canada’s oil sands.

The grounds and buildings behind the 143-year-old iron gates are patrolled by RCMP officers and government security guards on foot and in vehicles. It is also monitored via video by several law enforcement agencies from an RCMP facility about 20 kilometres east.

The airspace over Parliament Hill is a no-fly zone.

Still, there have been security breaches:

– In 1997, a Quebec man drove a Jeep up the steps of the Centre Block but stopped short of crashing into the main doors.

– In 1989, an armed man hijacked a New York-bound Greyhound bus near Montreal and forced the driver to go to the front lawn of Parliament Hill, where the gunman held several passengers hostage for six hours. No one was injured and the hijacker — who had demanded the release of political prisoners in Lebanon —  surrendered to police.

– In 1966, unemployed security guard Paul Chartier blew himself up in a washroom inside the Centre Block. According to reports, Chartier intended to toss dynamite onto the floor of the House of Commons but lit the fuse too soon.

The prime minister’s official residence, 24 Sussex, was breached in 1995. A man carrying a small knife made it to the bedroom door of Jean Chretien and his wife Aline.

The prime minister armed himself with an Inuit stone carving for protection until RCMP officers arrived.