One day, perhaps scholars will debate the exact moment in early 2011 when the scales tipped against Col Muammar Qaddafi, the four-decade ruler of Libya.
Maybe it was the first spark of revolt in the eastern city of Benghazi. Maybe it was protesters joyriding in captured army tanks. Maybe it was the desperate call for order from Col Qaddafi's son.
It is too early to tell whether the revolt that began last week will unseat Col Qaddafi, who has crushed opposition in the past.
Today he enjoys some popular support, oil wealth to assuage economic grievances and command of the armed forces.
However, those advantages appeared to be slipping from his grasp as violence spread on Sunday from outlying regions to the capital, Tripoli.
Reports of violence are difficult to verify. Authorities have tried to block internet and phone networks, while foreign media are barred from entering Libya and resident correspondents are confined to the capital.
Nevertheless, a picture of the violence has emerged via phone calls and postings on social media such as Facebook and Twitter.
Protests began last Tuesday in Benghazi, Libya's second-largest city, two days before a scheduled "day of rage" called by opposition groups to emulate revolts that have swept through Arab countries and toppled leaders in Tunisia and Egypt.
Within days, protests spread to other cities in Libya's east, a marginalised and historically restive area that has never fully accepted Col Qaddafi's rule. But on Sunday they reached Tripoli's Green Square, where snipers and pro-government militiamen fired on demonstrators.
The International Federation for Human Rights said between 300 and 400 people have been killed so far in the Libyan uprising.
Mr Qaddafi has not flinched in the past from using deadly force to get his way, whether against dissidents in Libya or in wars against Chad. For years, he also bankrolled a rogues' gallery of militant groups and liberation movements.
Early yesterday, Col Qaddafi's son, Saif al Islam Qaddafi, warned Libyans in a televised address that his father would fight attempts to oust him to "the last man, the last woman, the last bullet". He blamed protests on foreign machinations and promised dialogue on reform.
That speech, a rambling address that mixed threats with efforts to cajole, was part of a cascade of events over the last 48 hours that suggest that Col Qaddafi's grip on power is in danger.
Col Qaddafi seized control of Libya in 1969 in a coup that ousted a pro-western monarchy. Banning political parties, he restructured government as a system of committees with himself as "Brother Leader and Guide of the Revolution."
Col Qaddafi has since stayed on top by courting the allegiance of tribes that make up Libyan society, and juggling political factions. Libya's oil wealth provides money for easing social and economic woes, and has helped shield Col Qaddafi from diplomatic pressure.
Now, however, those foundations of Col Qaddafi's power appear to be crumbling.
The leader of the Al Zuwayya tribe, which lives south of Benghazi, threatened yesterday to cut off oil exports to western countries if Col Qaddafi continued to attack protesters. The large Al-Warfalla tribe has told Col Qaddafi to leave Libya.
The US president, Barack Obama, and the European Union's foreign affairs chief, Catherine Ashton, have also condemned the crackdown. The United Nations' secretary-general, Ban Ki-Moon, telephoned Col Qaddafi yesterday to urge an end to violence.
Col Qadafi's whereabouts last night were unknown.