A black mesh, said by police to be water repellant, covers the fence. Nets run up to the subway tracks, to prevent protesters from hurling debris over the fences. Razor wire curls along the tracks. The pen has only two exits, one of which appears to be no wider than an office doorway.

Cops say the pen can hold 4,000 people.

Inside the "Free Speech Zone," protesters are invisible and all but inaudible to delegates arriving in the parking lot nearby. Abandoning a plan to boycott the cage, some protesters say they will now turn it into a dramatic re-creation of Abu Ghraib, the prison where U.S. soldiers tortured Iraqis. Others are calling it Camp X-Ray, after after America's holding facility in Guantanamo Bay for prisoners in the war on terror.

Some anarchists still intend to protest outside the cage, risking arrest and the use of force by Boston police and the Secret Service, not to mention the National Guard troops that have poured into the city. For cops in situations like these, the tools of choice have become so-called nonlethal, or less lethal, weapons, from tear gas and pepper spray to rubber bullets and stun guns.

Some 40 volunteers from the Boston Area Liberation Medic (or BALM) Squad will be on hand to treat any wounded. "If you fail to turn your head away in time, and that rubber bullet or beanbag hits you in the temple or the throat, it can be lethal," said Sandy McKinley, an EMT and BALM medic.

So far, the Dems have shown only their contempt for the plight of their detractors. "People had the opportunity long ago to speak to their delegates," said a press aide for the convention committee. "There are plenty of other ways to make your voice heard other than protesting."

Now debate and its consequences are left to the cops, the protesters, and the BALM volunteers. "They have anything you'd ever need, from Band-Aids to eye flushes," said Tania Vamont, a member of the Boston Anarchist Black Cross.

BALM medics, in addition to wearing the red cross on their clothing, also wear a badge depicting the squad's logo: a snake coiled around a raised fist, set against a red "star of resistance."

"It's absolutely reassuring," said Vamont, "to see them in a crowded situation."