Richard Overy, a meticulous chronicler and a precise summariser, estimates that 600,000 European civilians died under bomb attacks in the Second World War. This is the equivalent to 200 consecutive days of September 11, 2001.
Of course, the attack on the Twin Towers had its very special horror, in that it was the first time New York had been assailed by air, and the sense of shock was heightened by the sheer unexpectedness of the act of terrorism.
Yet if one justifiably still reels at the images from the city 12 years on, what must it have been like to have been in Dresden on February 13-14, 1945, when more than 700 Lancaster bombers carrying 2646 tonnes of bombs achieved what Overy describes as "an exceptional level of concentration".
A firestorm erupted and consumed about 25,000 people. Overy, in a magisterial account of a sprawling campaign, cannot be more exact. A firestorm has the effect of both reducing some bodies to ashes and mummifying others. Some estimates of death were made by weighing ashes and guessing how many people amounted to that mound of dust lying under rubble.
Dresden, of course, did not suffer this grisly fate alone. Hamburg, too, suffered grievously from a firestorm, with up to 30,000 dead, and London was blitzed, Stalingrad almost razed, Caen bombed almost into dust by the forces seeking to liberate it and, more locally, Clydebank was pounded in the spring of 1941.
Overy does not seek merely to weigh the tonnage of bombs or count the dead but to judge the impact of bombing campaigns on the course and the outcome of the war. His conclusions are rigorously achieved and carefully articulated.
A crude summary is that the bombing campaigns strangely had a limited effect on the morale of civilians, were regularly wasteful both in terms of the percentage of bombs finding targets and in the high death rate of attackers, but were perhaps most effective in easing the way for ground troops (though this was not always the case as the destruction of Stalingrad, for example, undoubtedly hampered the German troops trying to take the city).
The case of Clydebank perhaps makes a general point. Only a few days after the town had been hit, major firms reported that two-thirds of their workers were already back at work. Others would return more slowly and six per cent would never come back, lost through death or flight.
Industry, though, kept churning out the materiel that would consume other cities and other workers, but would never wholly render the Ruhr or London or Coventry or Normandy incapable of sustaining life and work. This is the dynamic at the heart of a remarkable book: how to make sense of a campaign that was impervious to human suffering and drained the resources of attackers, yet did not have the cataclysmic, conclusive effect its proponents insisted was its main purpose.
It is made clear that the inhabitants of London, Clydebank or Berlin were not bombed into submission. They mostly railed at their political masters - whether Churchhill or Hitler - for allowing such a fate to fall upon them, but largely they went back to work and, indeed, went back to their homes, no matter how damaged.
The inception of the bombing campaigns is also investigated. Intriguingly, Overy points out that Churchill did not just react to German raids on British cities but, in the manner of an old-style centre half, "got his retaliation in first". He saw this as a theatre in which Britain, dismally racking up defeats in the ground war, could demoralise the German population while raising the morale of his country.
But the British prime minister became disillusioned with the impact of bombing cities. He put it thus in one memo to Lord Beaverbrook: "Even if all the towns in Germany were rendered uninhabitable, it does not follow that the military control would be weakened or the war industry could not be carried on."
This was written in 1941, yet the bombing of civilian targets continued. The reasons are various. Dresden was looked upon as the congregating point for any concerted retreat by the German army. Hamburg was a port and, crudely, easily found by following the coastline.
There was also an undoubted element of "paying the Germans back" for raids. This was voiced by Churchill when he advocated "absolutely devastating, exterminating attack by very heavy bombers from this country on the Nazi homeland". Arthur Harris, of Bomber Command, took these words as his orders for the prosecution of a war that produced unprecedented carnage from the air and in the air.
Incidentally, one of the strengths of this powerful book is the examination of how the bombing war was extraordinarily lethal to those who conducted it. Crews routinely failed to complete missions because they could not find cities and, when they did, often missed their intended targets by miles. This did not prevent them from being shot down by fighters or artillery or being incapacitated by weather conditions. There is one scene when an airman notices that bits of his plane are slowly falling off because they have been hit by ice.
The struggles and suffering of both the attackers and their victims produces passages in the book of immense suffering that go beyond the arithmetic of those killed or wounded. It is the sheer desperation of the conflict that becomes clear through the mass of statistics on tonnage, victims or amount of aircraft. This was a fight for survival and it reduced politicians, civilians and airmen to elemental concerns.
It also produced the spectre of gas warfare. The RAF had already made plans for such attacks early in the war and the Allies were braced in 1945 for Germany to launch an offensive with sarin and tabun, both nerve agents, as it faced the inevitability of defeat. Mercifully, these did not materialise. However, two atom bombs were dropped on Japan, a subject outside Overy's specific remit.
His researches, though, prompt a series of reflections. It would seem that bombing fuel dumps rather than cities would have been more influential on a quick resolution to the war. It is clear that the results of investigations into the campaigns were not used to the best advantage of attacker or victim.
But war is not always conducted by cool heads. There was fear and anger in the minds of civilians, airmen and, crucially, the political leaders. Bombing was not just a strategy but a punishment. It was civilians - whether huddled in shelters or sleeping at home or working in factories - who paid the price.
There are many stories about bombing wars but that is the enduring one.