When Lebanon's Hezbollah first joined Syria's war on the side of President Bashar Assad, its role was a closely guarded secret. Today, as Hezbollah plants its flag in land won from rebels north of Damascus, its role could hardly be more public.
And for Syria's increasingly embattled president, Hezbollah's help is more critical than ever.
In the last week, the Iranian-backed guerrilla group has unleashed its powerful arsenal to drive insurgents from wide areas of the Qalamoun mountain range, a short drive from Assad's seat of power in Damascus.