In the entire history of the United States only five of its ambassadors have been murdered, the last in 1979. So the killing of Chris Stevens in Libya is significant in historic terms. But in other ways too, this is a critical event.
It's now clear that the attack was far more serious than previously thought. Stevens and three other US Embassy staff died trying to escape in their car from a consulate that was attacked for as long as five hours. Libya's Deputy Interior Minister claims another eighteen Americans were injured, though such figures can't be taken as fact.
Stevens was an old Libya hand, arriving in the country first in 2007, serving for two years. He came to Benghazi on board a cargo ship at the height of the uprising, establishing America's link with the rebels who are now Libya's new rulers.
America's role in arming the rebels and acting as its air force has now been repaid; its ambassador has been murdered.
It will have an effect on future US policy in the region. In Washington today they will be even more cautious about helping Syria's rebels in any military way - especially arming men who may later turn their weapons on Americans, as happened in Afghanistan, as happened last night in Benghazi.
It won't have gone unnoticed that the attack came on September 11th - on the eleventh anniversary of the attacks on New York and Washington.
The groups who attacked the Benghazi consulate have links with Al Qaeda, beginning with the area where they're from; Eastern Libya provided many of the Al Qaeda recruits who went to attack Western troops in Iraq.
The attack has global implications. President Obama says he has ordered increased security at diplomatic posts "around the globe," America fears, rightly, attacks on its embassies, in the Middle East especially.
Islamist radicals in Tunisia have called for attacks on US facilities. It's not clear yet whether the attack was long planned by Islamist groups determined to exploit any opportunity to target Western interests or whether it grew from the fury of a crowd held back from its goal by the bullets of a poorly deployed Libyan security force. But in Afghanistan, Indonesia, the Gulf and elsewhere, American diplomats will be taking more care of where they go and who they see.
The attack exposes two things; the lack of authority Libya's new government has on the ground. Militias still bristle with weapons; towns remain out of reach of central government's writ and gratitude to NATO for its role in the revolution has given way in some places to Salafist resentment at its government's continued alliance with the hated and decadent West.
But the storming of the consulate also demonstrates the gulf between the West's freedom of expression and the Islamic fury at anything that is said against the Prophet Mohammed.
The American movie, made by a man who identifies himself as an Israeli Jew and who says Islam is a cancer, is designed to "expose Islam's flaws" and, frankly, to insult the religion.
In the new Middle East; in an Egypt that is still a cauldron of competing views of Islam's role in government; in a Syria in open war, and in an Iran that is braced for a Judeo-Christian attack on its nuclear sites, the film and the Benghazi attack that it provoked shows the huge and continuing gulf between the West and the region that it has been in conflict with for half a century.