Supervisors also ensured that none of the officers were carrying pepper spray or Tasers - weapons banned for the night - and made clear that force would be authorized only by their superiors. The protesters, they said, would be given every opportunity to leave the area before being arrested.
"These people are not criminals," said Chief Inspector Joe Sullivan, who oversaw the operation. "They are not our enemies."
Fisher noted that officers were taping the roll calls and would be filming throughout the night. Commissioner Charles H. Ramsey also reminded them that protesters would train cell phones and cameras in their direction - and said that was fine with him.
"If that happens, it happens," he said. "Smile for the camera."
While planning the massive operation, the department's top commanders admitted being mindful of the ugly police assault in Oakland, Calif., and the indelible image of a California campus officer casually pepper-spraying seated demonstrators - and the contrast the Philadelphia police had established so far.
"The main thing will be trying to keep the whole tenor of what's been going on," said Deputy Commissioner Richard Ross. "We're not looking to go in like storm troopers. We're most interested in resolving this peacefully."
At the roll calls, held for various units at the police academy on State Road, commanders set lofty goals for the night - clear the plaza with no arrests and no injuries, and finish the job before the morning rush hour.
"No force, no arrests, that's a grand slam," Sullivan said.
If not for the $50 million renovation of Dilworth Plaza, Ramsey said, the protesters might not have been cleared out Wednesday morning. But Mayor Nutter had given the occupiers until 5 p.m. Sunday to make way for construction crews, and a segment of the protesters had ignored the deadline.
The police operation involved hundreds of officers from multiple units. Outreach workers were on hand to assist the homeless in the encampment - Nutter said 15 people were moved into shelters Wednesday morning.
SEPTA buses were available for protesters who needed transportation. Sheriff's buses were on hand for those who insisted on being arrested.
Patrol officers, mustering at the Fairmount Waterworks, began by shutting traffic from Arch to Chestnut Streets and 13th to 16th Streets. The enormous caravan of personnel and equipment at the police academy began snaking down I-95 about midnight.
"This could go one way or the other, but we're confident we got a good plan in place, and we'll execute it," Ramsey had said earlier in the day. "We can't control what they do, but we can control what we do and how we respond. . . . If they want to turn it ugly, we've got to go along with them. But they will get off Dilworth Plaza."
During the trip to Center City, Karima Zedan, the department's director of strategic communications, monitored the chatter on social media of a building police presence at City Hall. Zedan and Ramsey discussed whether they should send the occupiers a message through the department's Twitter feed, which they knew the protesters monitored.
"What we should say is just what our goal is, and that's to safely remove people so construction can begin," the commissioner said.
As Ramsey's Car 1 arrived at City Hall about 1 a.m., Zedan sent the tweet.
The elite Highway Patrol and Narcotics Strike Force officers who would be responsible for clearing the plaza and making any arrests were broken into two teams, each headed by an inspector and a captain. After the plaza was cleared, officers with medical and hazardous material training would move into the encampment.
The commanders expected occupiers to mass on the plaza to be arrested. Instead, after Fisher gave them a final warning to move, a large contingent bolted south on 15th Street. A smaller faction crossed the street to chant and shout.
No one was arrested, and the plaza was cleared of people in minutes.
The larger group of protesters ended up outside the police cordon, and would spend much of the night in a cat-and-mouse game with officers, especially the bicycle cops who shadowed them as they searched for a way back to City Hall. Protesters and officers clashed occasionally at barricades around the perimeter of City Hall.
Back at Dilworth, Ramsey walked through the encampment and peeked into some of the empty, cluttered tents.
"I knew it was bad outside, but I never looked inside," he said. "Geez." The group of protesters across Dilworth pushed into the street and linked arms. Officers approached, and then backed off.
"It's 2 o'clock in the morning," Ramsey said. "We don't need the street. Let them stand there." Eventually, the group was encircled by bicycle officers and Fisher gave the standard three warnings to disperse. After the last warning, six protesters remained to be pried apart and arrested.
Shortly after that, officers on horseback confronted protesters to push them back to the sidewalk. One horse charged briefly, stepping on a protester's foot. Nutter said that was the night's only injury to a protester, but Occupy members said others were hurt in that incident and other clashes.
The horse's charge sent the protesters scattering in a moment of chaos that was captured on television and amateur video. It was unclear if the horse was frightened or provoked, or if the officer intentionally drove the animal forward.
Either way, Ramsey said, the horse "shouldn't have gone up on the sidewalk."
About 4:30 a.m., sanitation workers were clearing the debris on the plaza, and police were dealing with the last protesters, who had moved to North Broad Street. With the morning rush approaching, police were pushing them north and attempting to clear the street.
"We can't do this all night," Ramsey said. "We'll have to box them in at some point." Clashes and curses between the groups were frequent during the slog up Broad Street. Two officers suffered minor injuries while making arrests.
Occupiers hooked a left on Spring Garden Street and another on 15th Street. Police stopped the march behind the School District of Philadelphia building, brought in the sheriff's buses, and created a gauntlet of bicycles.
More than 40 protesters amassed along a wall on 15th with their hands up. Fisher brought them out orderly, one at a time, to be cuffed and searched. By 5:20 a.m., the last arrest had been made and the rest of the protesters wandered back to the Friends Center on Cherry Street, one of their frequent gathering spots.
At a press briefing about an hour later, Mayor Nutter praised police for a "tremendously well-planned and well-executed operation." Meanwhile, bulldozers were scraping up the last of the tents and debris on Dilworth while workers - some in white hazmat suits - hosed down the concrete.
Throughout Wednesday, the Occupy Philadelphia Facebook page filled with numerous complaints of police aggression, including officers choking protesters, using bikes and barricades as weapons and shoving people into walls.
"These actions of brutality, force, and disrespect for human life and the First Amendment are what Mayor Nutter calls: professional, restrained and disciplined," said one Facebook entry.
Certainly, the operation did not hit Sullivan's "grand slam" of no arrests and no force, but Ramsey said the arrests were unavoidable and he was pleased with the outcome.
"I think we showed remarkable restraint and patience," he said. "They weren't exactly orderly. They were very confrontational."
For more photos and video of the cat-and-mouse game between police and protesters, click here.
Contract staff writer Troy Graham at 215-854-2730, firstname.lastname@example.org, or @troyjgraham on Twitter.