Islamic State jihadists in Syria have for months expanded their field of operations beyond their “caliphate” in the north-east of the country.
But now they are fighting for the Yarmouk Palestinian refugee camp in the capital, one of the most internationally recognised symbols of the conflict . If they win, they will have a mile-square base of operations just five miles from the centre of Damascus itself.
That is within the range of their rockets, threatening President Bashar al-Assad’s power base with daily attack .
This does not mean that Isil poses an immediate threat to the regime. The group does not have the numbers in the south of the country for that.
In fact, it does not have the numbers to overwhelm other rebel groups, who have occupied areas of the northern and eastern suburbs for years now, and drove out a previous attempt by the jihadists to muscle in.
However it is increasingly confident in what is a new tactic, one that is proving very hard for both the regime and competing rebels to challenge. It establishes a cell - one that is not immediately large enough to be a threat worth taking on.
Then it strengthens it until taking it on would become too painful, thereby establishing dominance over a small area.
Charles Lister, who speaks regularly to rebel groups across the country as an analyst for the Brookings Institution, said Isil applied this tactic to a suburb next to Yarmouk called Hajar al-Aswad.
By the time it moved on to Yarmouk, it had enough sway to be able to raise its black flag.
As has been pointed out repeatedly, there is nothing in Syrian history to suggest large numbers of people welcome its millenarian, violent fantasies.
However, it does have a record of enforcing authority and providing some basic services - something that might appeal to the residents of Yarmouk, who have been shelled and starved to within inches of their lives by a regime siege.
There is also a widespread belief - not without some foundation - that the regime holds off from bombing areas controlled by Isil.
In this way, Isil can gradually establish nodes around the country, even as its core territories come under attack from the allied international coalition in the air, and Kurdish and other militia forces on the ground.
That accounts for the conundrum that while in Iraq, where a concerted, conventional war is being fought against it, it appears to be losing, but in Syria it is still on the march.
The stage is being set, too, for something much broader.
All talk of the regime “winning the war” - the vogue idea being circulated for a year from late 2013 - has disappeared.
In recent weeks, it has lost another provincial capital - Idlib, in the north-west - and border areas with Jordan. Its attempts to dislodge the rebels from those Damascus suburbs has failed, and it is losing serious ground in the central Syrian provinces of Homs and Hama which it thought it had secured.
The difference between now and the earlier period of the war when its existence seemed to be at threat is that almost all the forces ranged against it now are led by militant Islamists.
Idlib was taken by a coalition led by Jabhat al-Nusra, the Syrian wing of Al-Qaeda, and Ahrar al-Sham, a hardline but Syria-focused Salafi group. Jabhat al-Nusra was also able to raise its flag on the border with Jordan.
Jaish al-Islam, the dominant force in the Damascus suburbs, is backed by Saudi Arabia and eschews the anti-western rhetoric of other groups, but remains an Islamist-dominated militia. Its leader, Zahran Alloush, was among the Islamist prisoners released by the regime at an early stage of the uprising.
With Isil also now established in parts of Damascus, as well as the north-east, the stage is being set for the next round of this apparently endless conflict, in which the regime retreats to its core areas, and the rest of the country becomes a battlefield for competing brands of Holy Warrior.
