Russia is staging its biggest military parade, marking 70 years of victory over Nazi Germany in World War Two.
Thousands of troops are marching on Red Square in Moscow, and new armour being displayed for the first time.
More than 20 heads of states are in Moscow, but many world leaders are boycotting the event because of Russia’s role in the Ukraine crisis.
As the event began, President Vladimir Putin said international co-operation had been put at risk in recent years.
In his speech, President Putin paid tribute to the sacrifices of Soviet troops during World War Two.
He also thanked “the people of Great Britain, France and the United States for their contribution to victory”.
But he added: “In recent decades the basic principles of international co-operation have been ignored ever more frequently. We see how a military-bloc mentality is gaining momentum.”
The remarks echo previous complaints by Mr Putin about what he says are efforts by the US and its Nato allies to encircle Russia militarily.
The victory parade started at 10:00 local time (07:00 GMT). Chinese President Xi Jinping, President Pranab Mukherjee of India and UN Secretary General Ban Ki-moon are among more than 20 world leaders watching the event.
Military units from across Russia – some dressed in WWII-era uniforms – are marching, and more than 100 aircraft have flown over Red Square.
The most talked-about new high-tech Russian armour is the T-14 Armata battle tank, which has a remote-controlled gun turret and reinforced capsule for the crew.
The RS-24 Yars intercontinental ballistic missiles – each capable of delivering three nuclear warheads – were also on show.