Damascus:
Russia, which launched its first air strikes in war-torn Syria on Wednesday, has been an ally of Damascus and had a military presence in the country since the Soviet era.
Moscow is a staunch diplomatic and military supporter of President Bashar al-Assad.
Here are key dates in relations since the Syrian conflict began in 2011.
'2011'
April 27: Russia and China block a proposed United Nations declaration that would condemn Bashar al- Assad's crackdown on the Syrian opposition.
October 7: Russia's then-president Dimitri Medvedev says Syria's regime should carry out reforms or step down, but emphasises the decision cannot be taken by NATO members or allied European governments.
'2012'
January 8: A Russian naval battle group arrives in the Syrian port of Tartus for a six-day visit to underscore support for the regime. In April, Russian media report Moscow will deploy ships permanently off the Syrian coast.
June 30: World powers meeting in Geneva agree on a transition plan for Syria in which Western powers see no role for Bashar al- Assad. Russian Foreign Minister Sergei Lavrov says Syrians will decide how to implement the transition, after which the plan goes nowhere.
October 10: Turkey intercepts a Syrian plane suspected of carrying Russian arms for Syrian armed forces.
November 27: Medvedev, now prime minister, says Moscow has "good working relations" with Assad, but not the "privileged relation" that existed with his father Hafez al-Assad.
'2013'
August 21: Russia dismisses Syrian opposition claims that a regime chemical weapons attack killed more than 1,300 people.
September 14: Russia and the United States agree to a deal under which Syria's chemical weapons are to be dismantled, defusing a crisis that might have led to United States-led strikes against Syrian forces.
2014
May 22: Russia and China veto a draft United Nations resolution to refer Syria to the International Criminal Court for crimes committed by both sides in the civil war.
2015
March 27: Bashar al- Assad welcomes a larger Russian military presence in the country's ports.
August 25: Bashar al-Assad says he is sure of Moscow's support after the United States suggests that Russia and Iran might drop him.
September 15: Russian President Vladimir Putin vows to keep providing military support for Syria to fight "terrorist aggression". Washington tells Russia that its backing for Assad risks exacerbating the conflict and undermining the United States-led campaign against the Islamic State group, calling for the Syrian leader to step down.
September 28: Putin calls in his speech to the United Nations General Assembly for a broader United Nations-backed coalition to replace the current United States led grouping of Western and Sunni regional powers bombing Islamic State jihadists.
Under his proposal the West and its partners in the region would join forces with Bashar al- Assad to fight Islamic State group and then try for a political solution in Syria.
September 30: In response to an appeal from Assad, Russia launches its first air strikes in Syria after Putin wins parliamentary permission to use force abroad.
It is Moscow's first military engagement in a distant theatre of war since the Soviet invasion of Afghanistan in 1979.