Mount Royal is the deep extension of a vastly eroded ancient volcanic complex, which was probably active about 125 million years ago.

[2] By a process known as intrusion, magma intruded into the sedimentary rocks underneath the area, producing at least eight igneous stocks.

During and after the main stage of intrusion, the gabbros and surrounding rocks were intruded by a series of volcanic dikes and sills.

[5] In 1876, land owner and farmer James Swail began planning residential subdivisions on the western slope of Mount Murray, in what is now the Cote-des-Neiges district.

The area was briefly considered as a candidate for the site of Expo 67 before the exposition grounds were ultimately built on adjoining islands in the Saint Lawrence River.

[12] From the point of view of the flora, the mountain shelters a set of natural spaces and semi-natural rich in trees, shrubs and herbaceous plants[13] The first Mount Royal Cross was placed there in 1643 by Paul Chomedey de Maisonneuve, the founder of the city, in fulfillment of a vow he made to the Virgin Mary when praying to her to stop a disastrous flood.

Today, the mountain is crowned by a 31.4-metre-high (103 ft) illuminated cross, installed in 1924 by the Société Saint-Jean-Baptiste and now owned by the city.

[14] The mountain is the site of Mount Royal Park (French: Parc du Mont-Royal), one of Montreal's largest greenspaces.

[19] The lush forest has been badly damaged, both by Mayor Drapeau's so-called morality cuts of the 1950s and by the Ice Storm of 1998, but has since largely recovered.

The forest is a green jewel rising above downtown Montreal and is known for its beautiful autumn foliage as well as its extensive hiking and cross-country ski trails.

Recently, the tradition has been revived as the Tuques Bleues celebration by the Les amis de la montagne, a charitable organization that works to protect and preserve the park.

Despite initial resistance by participants, the city now intervenes in the event, restricting commercial activity to registered members in designated areas and assigning police and first aid technicians to ensure the safety of those present.

Although initially controversial in light of the event's communal and countercultural vibe (as well as a permissive attitude towards then-illegal cannabis use), the police presence has not led to conflict.

A popular recreational area, Jeanne-Mance Park features a playground, a wading pool, tennis courts, various sports fields, and in winter, a skating rink.

The engineering challenge was to combine all the desired antennas in the limited space between the mountain top and 1100 feet above sea level, which led to the "candelabra" design.

Outside the park, Mount Royal's slopes are also home to such Montreal landmarks as Saint Joseph's Oratory, Canada's largest church; McGill University; the Montreal General Hospital; McGill's Molson Stadium, home to the CFL's Montreal Alouettes; the McTavish reservoir; Université de Montréal; the École Polytechnique de Montréal; the Îlot-Trafalgar-Gleneagles historic block;[38] and some well-off residential neighbourhoods such as Upper Westmount and Upper Outremont.