Protesters attacked in Bahrain by police as they prepare to go to sleep.

Without warning, hundreds of heavily armed riot police officers rushed into Pearl Square here early Thursday, firing tear gas and concussion grenades at the thousands of demonstrators who were sleeping there as part of a widening protest against the nation’s absolute monarchy.

Men, women and young children ran screaming, choking and collapsing.

The square was filled with the crack of tear gas canisters and the wail of ambulances rushing people to the hospital. Teams of plainclothes police officers carrying shotguns swarmed through the area, but it was unclear if they used the weapons to subdue the crowd.

Only hours before Thursday’s crackdown on the protests, the square had been transformed from a symbol of the nation — anchored by a towering monument to its pearl-diving history — into a symbol of the fight for democracy and social justice that has been rocking autocratic governments all across the Middle East. Tens of thousands of people had poured into the square during the day, setting up tents, giving rousing speeches and pressing their demands for a constitutional democracy.

Bahrain is an odd little country - I got to visit when I was touring Saudi Arabia. It's an island that is connected by causeway to Saudi Arabia, and the affluent drive over on the weekend to enjoy the looser social environment. There are western style restaurants in Bahrain that serve alcohol. The monarchy treats the country like a private clubhouse, and they benefit from being subsidized by the Saudis with a small pipeline that feeds a steady supply of oil across the causeway.