"Boston really changed things," said Samantha Phillips, the city's director of emergency management.
Sunday's marathon will kick off at 6:57 a.m., but the course will open about 4:30. Organizers have advised starting-line spectators and runners alike to arrive early to allow themselves time to make it through security checkpoints.
Those checkpoints will be set up between 20th and 25th Streets on the Benjamin Franklin Parkway - an area organizers have termed a "Secure Zone."
Volunteers will screen runners and spectators entering the zone, organizers said, and backpacks and coolers are prohibited.
Runners can take only special marathon-issued clear bags into the race area, which were distributed starting Friday.
Outside the Secure Zone, spectators can carry backpacks and will not have to pass through a security checkpoint. But Philadelphia police will be stationed along the rest of the 26.2-mile course, Chief Inspector Joe Sullivan said.
Officials will monitor the course with the help of a helicopter and a slew of surveillance cameras positioned along the route, which winds down the Parkway and through Old City, Center City, Fairmount Park, and Manayunk before finishing back on the Parkway.
"Do not leave anything unattended," Sullivan said. "It will not be there for long."
SEPTA transit police will also have an increased presence in the area on race day, SEPTA spokesman Andrew Busch said.
Those traveling through Center City, he said, are advised to use subways and trains when possible. About 28 bus routes will be detoured during the marathon, and SEPTA will have transportation managers on hand at subway stops to assist bus riders who are unfamiliar with the subway, he said.
Details about the rerouted buses and information on alternate routes are available online, Busch said.
City officials said they have made several changes to security procedures since April - and added that the Broad Street Run, held just weeks after the Boston bombings, served as a trial run for security at the marathon.
"The level of preparation and the level of participation didn't happen last year," said Mark Resnick, the deputy mayor of public safety. "The Broad Street Run was a good testing ground."
Still, the Broad Street Run wasn't without its own challenges. Traffic from a late-afternoon Phillies game, combined with a major accident on I-95 and 10 miles of Broad Street blocked off for the race, led to backups across the city and more than a few frustrated residents.
Philadelphia police have been receiving daily intelligence briefings from the FBI on potential threats, Sullivan said. Officials would not comment on the amount of extra manpower at the event.
Organizers are encouraging spectators to be vigilant as well, Sullivan said.
"If they see anything unattended or anything suspicious," he said, "they should call 911. A police officer will be there in seconds."
At a news conference Friday afternoon, Mayor Nutter welcomed runners to the city and officially opened the marathon weekend.
The city, he said, is always looking to improve safety.
"Every year, we've had some kind of enhancement to security," he said. "We try to learn from each event."