One of the most important unanswered questions in the search for an end to Syria’s bloody war concerns the durability of the alliance of convenience there between Moscow and Tehran. The remarkable sight of co-ordinated Russo-Iranian operations in Syria belies what had been a century of mistrust and suspicion between them. Relations thawed after the fall of the Soviet Union, but the countries’ long-term goals still diverge markedly. Syria is expected to be one of the top agenda issues for President Vladimir Putin when he travels to Tehran on Monday — the Russian leader’s first visit in eight years and the first since Hassan Rouhani became Iranian president. Christopher Phillips, a Syria expert at Chatham House international affairs think-tank in London, describes Iran and Russia as “frenemies” in Syria, fighting in lock-step for a common short-term interest but maintaining divergent long-term goals.