More than its weapons sales to the regime of Syrian President Bashar al-Assad, Russia's greatest strategic and geopolitical interest in Syria is the use of a deep-water port at Tartus. RFE/RL takes a closer look at this arrangement.
How long has Moscow been using Syria's port at Tartus as a strategic naval base in the Mediterranean?
The Soviet Navy began using Syria's deep-water port at Tartus for submarines and surface vessels under a 1971 agreement with Damascus. The Soviet Union was Syria's main arms supplier and Tartus was used to receive Soviet weapons bought by Damascus.
The Soviet Fifth Mediterranean Squadron also used the docks at the base to load its own fuel and supplies.
The Soviet Navy had similar support points in Egypt, but the Soviets evacuated the Egyptian bases in the late 1970s, sending ships and equipment to Tartus instead.
That transformed Tartus into the Soviet 229th Naval and Estuary Vessel Support Division. In the mid 1980s, Tartus was upgraded to become the 720th Logistics Support Point for the Soviet Navy. The Russian Navy continued using Tartus after the Soviet broke up in 1991.
How has Russia managed to maintain a presence at Tartus after the collapse of the Soviet Union?
By 1990, Syria had built up debts of $13.4 billion to Moscow largely due to weapons purchases by Damascus.
In May 2005, Russian Finance Minister Aleksei Kudrin signed a deal with Syrian Finance Minister Muhammad al-Hussein that wrote off 73 percent of Syria's Soviet-era debt.
Russia ensured that it continued to have base rights at Tartus under the 1971 treaty as a result of the debt write-off deal, which cleared the way for Damascus to make fresh weapons purchases from Russia.
In terms of logistics, how does Russia's presence at Tartus bolster Syrian President Bashar al-Assad's regime?
Tartus is the receiving point for Russian weapons shipments to Syria. The port is the country's transport hub for newly purchased arms as well as for weapons that must be returned to Russia for repair, such as attack helicopters.
The port is linked inland to a well-developed network of roads and highways.
Syria's only railway passenger connection from Tartus is linked to the port of Latakia further north.
However, the national railway operator, Chimins de Fer Syriens, also operates military transport routes from Tartus to major cities across Syria.
How does Tartus serve Russia's strategic and geopolitical interests?
Even a semipermanent base at Tartus allows the Russian Navy to expand its presence in the eastern Mediterranean Sea.
Russia's largest and most important military base in a foreign country is the Black Sea Fleet base in Sevastopol, Ukraine.
To deploy beyond the Black Sea, Russian warships based at Sevastopol must pass through the Bosporus Strait, which has been militarized by NATO-member Turkey.
Under the 1936 Montreux Convention
, the Bosporus was deemed an international shipping lane with military restrictions. Under a 1982 amendment, Turkey now retains the right to close the Strait at its discretion in peacetime as well as during wartime.
As Russia's only Mediterranean base, that makes Tartus a vital strategic asset beyond the Bosporus.
As a deep water port, it can dock nuclear submarines.
Moscow is reportedly planning to expand the facilities so it can accommodate the Russian Navy's flagship -- the "Admiral Kuznetsov" aircraft carrier -- after 2012.
Tartus also strengthens Russia's great-power aspirations and increases its influence in regional diplomacy.
Could Russia's use of Tartus be affected by the ouster of Assad's regime?
Analysts agree that Russian vetoes of UN Security Council resolutions against Assad's crackdown on dissent, as well as Russian weapons sales to the regime, make it likely that an opposition government replacing Assad would try to strip away Russia's rights to use Tartus.
Last autumn, as popular opposition to Assad's regime was growing, Russia took steps to expand basing rights for its warships in Venezuela.
It also deployed a naval task force to Tartus, led by the "Admiral Kuznetsov" aircraft carrier, which is staying nearby for what Moscow describes as a long-term training mission in the Mediterranean and Atlantic.