That row of Land Rovers stretched across the Woodvale Road since the Twelfth is no ordinary police line. It is a statement of so much more: the row is a message that the Chief Constable, the PSNI and the reinforcements from elsewhere in the UK are going to stand their ground and do what has been determined by the Parades Commission.
So, this is a big test; not just on this one march decision, but for the new policing project. Matt Baggott is not going to force a change to that decision to block the return Twelfth feeder parade from passing Ardoyne.
He is not going to go to Secretary of State Theresa Villiers to ask her to intervene, something that would first require him to make a dire security assessment.
So, it doesn't matter whether there is two nights of rioting, or 20 nights of rioting. A decision has been made, and it is going to be policed. This is not 1996, or 1997, when previous chief constables Sir Hugh Annesley and Sir Ronnie Flanagan, became part of the parading controversy over decisions they took at Drumcree.
Marching decision-making now rests with the Parades Commission. The PSNI role is simple – to police the ruling, whether it is a decision to allow a march to proceed, or to block it.
That the latter was the decision was something not publicly announced until late last Tuesday evening, but the likelihood of that ruling was known days before then. And, in the background, there was a commentary about consequences, talk of an 'Armageddon' scenario.
The interventions were clearly designed to force a re-think – interventions from those who always know best and know better.
There was a clear purpose: that the chief constable and secretary of state would buckle and then the marching decision would be reversed. "Not a chance," was Matt Baggott's response when I spoke to him early on the Twelfth morning in north Belfast. "That's why the mutual aid is here," he said, referring to the hundreds of additional officers he has brought in from other UK forces.
And this move also is about protecting the progress made so far in the peace process; keeping the military option out of the picture, choosing police and not soldiers as support.
Watching in recent days, I have seen that those mutual aid officers have not been some bit-part player. They have been in the difficult, tight spots; some have been hurt and others have been completely thrown by the complexities of the marching stage.
As a PSNI officer was lectured on Friday by irate Orangemen after a woman with a child in a pram were escorted across the road, I listened as an academic explained the unwritten rule of not breaking the ranks of the parade without permission.
He was talking to one of the many police visitors at the junction of Clifton Street, Carrick Hill, North Queen Street and Donegall Street; explaining what, anywhere else, might appear to be nonsense.
As he spoke, the officer admitted that the nuances of these parading procedures would go straight over his head. The mutual aid officers know how to police, how to hold lines, but how could they possibly begin to understand the fine detail peculiarities of Northern Ireland?
On Friday and Saturday, I watched the police lines being pelted at Woodvale, and the calls for peaceful protest and civil disobedience disappear beneath a blizzard of bricks, bottles, golf balls and petrol-bombs.
I watched this scene become an angry, violent confrontation and watched young people being left on this riotous frontline, left with the consequences of their actions.
Arrests, charges – maybe prison; all of it happening at a police line that wasn't going to be broken or breached, and all of it happening as others walked away.
This is not a re-run of the Drumcree crisis of the 1990s; it is not a redrawing of those scenes of mass protest that are remembered from that period.
There are not thousands of soldiers on the streets in support of policing.
Up to this point, there is no indication that there is a mood for widespread and sustained violence.
The past few days have been about a short stretch of road in Belfast where that police line has been put in place; a line that has held and will continue to hold.
Because it has to.
Hundreds upon hundreds approached it on Friday night from the loyalist side, and, not far away, a significant crowd had gathered at Ardoyne.
So the consequences of the line being broken are obvious. It can't, for many reasons; community safety, protecting the new policing project, not buckling to the old ways and old pressures.
But for how long will the police have to stand on that road and at the other flashpoints within that small, unshared area of north Belfast?
For as long as they have to is the answer to that question, but their presence says something else.
It is a reminder of political and community failure; that the police are there because we have an unfinished peace and unanswered questions.
The PSNI and the mutual aid officers are holding the line and their nerve.
But the political noise is all too familiar – disagreement, blame, somebody else's fault and no answers to old problems.