Over the long, cold winter, Boston has been preparing a ceremony to honour those killed and injured in last year’s marathon and to stage a race that will be one of the biggest — and, they said on Monday, the safest.

The 118th running of the Boston Marathon, scheduled for April 21, has drawn a huge field of about 36,000 runners, which is capacity for the course and 9,000 more than last year. The runners include thousands who were forced to stop last year after the explosions and thousands more who want to show their solidarity with Boston. (The record number was set in 1996 at the marathon’s centennial celebration, when 38,708 runners entered.)

At least one million spectators, twice the usual crowd, are expected to gather along the 26.2-mile course, many of them at the finish line on Boylston Street, where two bombs exploded, killing three people and injuring 260 others.

The security challenge is immense, in part because the event is spread across eight cities and towns along a route lined by spectators on both sides. More than 3,500 police officers, twice the number of last year’s, will be deployed, public safety officials said here on Monday at a news conference outlining their security plans.

Despite the intense security upgrades, officials said they did not want Boston to appear to be a police state and they were trying to retain the festive and traditional character of the event, the oldest continuously run marathon in the world.

“We are confident that the overall experience of runners and spectators will not be impacted and all will enjoy a fun, festive and family-oriented day,” said Kurt N. Schwartz, director of the Massachusetts Emergency Management Agency.

On April 15, the date of last year’s Marathon, a procession of hundreds of people, including survivors of the explosions, families of the dead and emergency medical workers, will walk down to the finish line.

Wreaths will be laid at the sites of the two explosions. At 2:49, when the first bomb went off, churches throughout Boston will toll their bells, sounds that officials said would signal the region’s mourning and its renewal. — New York Times News Service