South Street, long one of Philadelphia's most popular venues, has always drawn a diverse weekend crowd and a wide array of wardrobes.

But last night, the most prominent fashion statement was the uniform - as in the police uniform. On foot, horse, and bicycle, more than 50 state troopers and Philadelphia police officers, including Commissioner Charles H. Ramsey, were on hand in an effort to avert a repeat of the May 30 debacle.

And a week after mayhem and violence rocked South Street, last night it was about as tranquil as the splendid June weather.

On May 30, as many as 10,000 youths, evidently lured to South Street by social-networking sites, overwhelmed surprised police officers. A cabdriver was carjacked, and two other people were pulled from their cars and assaulted.

At a police staging area at South and Passyunk Avenue, Lt. Gerry McShea declined to say precisely how many officers were on the street last night but did say the number was "significantly greater" than on a typical Saturday night.

On a warm, clear, and moonlit night, the crowds were about average for a Saturday, the only noticeable difference being fewer families with younger children in tow.

Police promised they would strictly enforce a midnight curfew for juveniles. Police said they believed that the region's teenagers were using social-networking sites, such as MySpace, to arrange huge gatherings.

Large numbers of youths have congregated at other times this year in University City and Upper Darby. However, they were not on a scale with the throng that showed up on South Street on May 30.

The dense South Street corridor from Second to Ninth Streets has a rich and sometimes troubled history.

It has long been one of the city's most alluring strips with its mix of idiosyncratic businesses, restaurants, and urban panache. While it has undergone many personality changes in the last 40 years, and arguably lost some of that edginess, it remains perhaps the most popular weekend destination in Center City, particularly among young people.

What happened last weekend was the most disruptive incident on the strip in eight years.

About 40,000 people showed up on South Street for Mardi Gras on Feb. 27, 2001. By nightfall, fighting had broken out, bottles had been thrown, and stores had been looted. In the end, 81 people were arrested.

Last weekend, several youths were arrested for curfew violations, but none for the violent incidents.

"There was no way we could have anticipated what occurred," Deputy Commissioner Kevin Bethel said Thursday during a community meeting.

That's understandable, Keith Ahn, manager of Lulu.ish, a trendy clothing and jewelry store, said last night. "It's so crowded at night, there's not always much that they can do," he said.