It's a message reminiscent of Hitler's call for General (later Field Marshal) Friedrich Paulus and his 6th Army to hold Stalingrad at all costs. Paulus attempted to win what became a battle of such brutality and attrition that it is still used to describe battles fought in spite of the fact that only one army can win.
Where Waterloo was a tactical masterstroke (coupled with luck and bad timing), Stalingrad would be pivotal, because it was the defeat that would turn the tide of World War II.
In that, Mosul could well become the Islamic State's Stalingrad. And as if to drive the point home, Abu Bakr al-Baghdadi, the leader of the Islamic State, issued his rallying call to his troops pinned down amidst the rubble of the city: "Do not retreat. Holding your ground with honour is a thousand times easier than retreating in shame."
"This raging battle and total war, and the great jihad that the state of Islam is fighting today only increases our firm belief, God willing, and our conviction that all this is a prelude to victory,"
To military historians, that will sound all-too-familiar.
In fact, according to latest reports, retreat, or even a break-out, may not be a viable option for Isis fighters anymore.
CNN is reporting that Shia militia involved in the offencive around Mosul have claimed to cut off an avenue of retreat for Isis fighters who remain in the city.
The Popular Mobilization Units (PMU) -- a largely Shia paramilitary force assigned the task of advancing west of Mosul -- say they have cut access to the main road leading from Mosul to western Iraq and toward Syria.
Whether the commanders of the forces encircled in Mosul take the orders to hold the city at all costs literally or not, one thing's for sure: When the Battle for Mosul enters its urban phase, the fallout will be bloody and the collateral damage immense.