And they're off! Boston Marathon elite begin course

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Elite Women Start Boston Marathon 2016

An elite field of runners from 11 countries began racing on Monday morning in the 120th Boston Marathon, the world's oldest continually run annual marathon.

It was the third running since a pair of ethnic Chechen brothers killed three people and injured more than 260 with a bombing attack at the finish line.

Ethiopian Lelisa Desisa will bid for his third title against 20 other competitors from nine countries, including two previous winners from Kenya.

On the women's side, Kenyan Caroline Rotich took to the course to defend last year's crown, but will face pressure from Ethiopia's Tiki Gelana, who won gold at the 2012 Olympics.

Most top U.S. marathoners are sitting out Boston to train for the Rio Games in August, but Kenya and Ethiopia have yet to pick their teams and will consider the Boston results.

The men's elite field took off from the starting line in the Boston suburb of Hopkinton at 10 a.m. EST (1400 GMT), about a half hour after the women's elite.

Tens of thousands of amateur competitors stretched and soaked up the sun, waiting to try the notoriously challenging course.

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And they're off! Boston Marathon elite begin course
HOPKINTON, MA - APRIL 20: Elite men leave the starting line in Hopkinton, Mass. of the the 119th Boston Marathon. (Photo by Bill Greene/The Boston Globe via Getty Images)
BOSTON, MA - APRIL 20: Caroline Rotich of Kenya celebrates after winning the 119th Boston Marathon on April 20, 2015 in Boston, Massachusetts. (Photo by Jim Rogash/Getty Images)
BOSTON, MA - APRIL 20: Lelisa Desisa of Ethiopa celebrates after winning the 119th Boston Marathon on April 20, 2015 in Boston, Massachusetts. (Photo by Jim Rogash/Getty Images)
BOSTON, MA - APRIL 20: (L-R) Caroline Rotich of Kenya, Mare Dibaba of Ethiopia, and Buzunesh Deba of Ethiopia run during the 119th Boston Marathon on April 20, 2015 in Boston, Massachusetts. (Photo by Maddie Meyer/Getty Images)
BOSTON, MA - APRIL 20: Caroline Rotich of Kenya celebrates after winning the 119th Boston Marathon on April 20, 2015 in Boston, Massachusetts. (Photo by Jim Rogash/Getty Images)
BOSTON, MA - APRIL 20: Caroline Rotich of Kenya, left, and Tirunesh Dibaba of Ethiopia race down Boylston Street during the 119th Boston Marathon on April 20, 2015 in Boston, Massachusetts. Rotich won the marathon with a time of 2:24:55. (Photo by Maddie Meyer/Getty Images)
BOSTON, MA - APRIL 20: Lelisa Desisa of Ethiopa (L) and Caroline Rotich of Kenya celebrate after winning the 119th Boston Marathon on April 20, 2015 in Boston, Massachusetts. (Photo by Jim Rogash/Getty Images)
BOSTON, MA - APRIL 20: Lelisa Desisa of Ethiopa celebrates after winning the 119th Boston Marathon on April 20, 2015 in Boston, Massachusetts. (Photo by Jim Rogash/Getty Images)
HOPKINTON, MA - APRIL 20: Blaise Brennan, of Millersville, Maryland gets a souvenir photo at the starting line in Hopkinton, Mass. before the 119th Boston Marathon. (Photo by Lane Turner/The Boston Globe via Getty Images)
HOPKINTON, MA - APRIL 20: Elite women leave the starting line in Hopkinton, Mass. of the the 119th Boston Marathon. (Photo by Bill Greene/The Boston Globe via Getty Images)
HOPKINTON, MA - APRIL 20: Runners roam the Athlete's Village at the Athlete's Village at the starting line in Hopkinton, Mass. before the 119th Boston Marathon. (Photo by Lane Turner/The Boston Globe via Getty Images)
HOPKINTON, MA - APRIL 20: A group from Wayzata, Minnesota takes a souvenir picture in the Athlete's Village at the starting line in Hopkinton, Mass. before the 119th Boston Marathon. (Photo by Lane Turner/The Boston Globe via Getty Images)
HOPKINTON, MA - APRIL 20: Race security personnel gather in the drizzle at the starting line in Hopkinton, Mass. of the the 119th Boston Marathon. (Globe staff / Bill Greene)
Runners cross the start line in the women's division of Boston Marathon Monday, April 20, 2015 in Hopkinton, Mass. (AP Photo/Stephan Savoia)
Runners cross the start line in the women's division of Boston Marathon Monday, April 20, 2015 in Hopkinton, Mass. (AP Photo/Stephan Savoia)
Runners cross the start line in the women's division of Boston Marathon Monday, April 20, 2015 in Hopkinton, Mass. (AP Photo/Stephan Savoia)
Explosive ordnance disposal officers walk near the finish line before the start of the Boston Marathon Monday, April 20, 2015 in Boston. (AP Photo/Charles Krupa)
BOSTON, MA - APRIL 18: Police patrol the starting area in Boston Common before the B.A.A. 5k on April 18, 2015 in Boston, Massachusetts. (Photo by Maddie Meyer/Getty Images)
BOSTON, MA - APRIL 18: Runners gather in Boston Common before the B.A.A. 5k on April 18, 2015 in Boston, Massachusetts. (Photo by Maddie Meyer/Getty Images)
BOSTON, MA - APRIL 18: Police patrol the starting line before the B.A.A. 5k on April 18, 2015 in Boston, Massachusetts. (Photo by Maddie Meyer/Getty Images)
BOSTON, MA - APRIL 18: Ben True of the United States wins the B.A.A. 5k on April 18, 2015 in Boston, Massachusetts. (Photo by Maddie Meyer/Getty Images)
BOSTON - APRIL 15: On the second anniversary of the Boston Marathon bombings, survivors Jeff Bauman, left, and Patrick Downes, right, threw out ceremonial first pitches before the game. The Boston Red Sox hosted the Washington Nationals in an MLB regular season baseball game at Fenway Park. (Photo by Jim Davis/The Boston Globe via Getty Images)
Gisele Schaaf, a runner from Long Beach, Calif., poses for a personal photo at the finish line, a day ahead of running in the 119th Boston Marathon, Sunday, April 19, 2015, in Boston, Mass. (AP Photo/Robert F. Bukaty)
Runners in the girls scholastic mile compete as part of Boston Marathon weekend activities in Boston, Saturday, April 18, 2015. The 119th Boston Marathon will be run on Monday. (AP Photo/Michael Dwyer)
Yaniv Kotcr, a runner from Boston, Mass., poses with his daughter, Noam, 2, at the finish line on Sunday, April 19, 2015, a day ahead of the 119th Boston Marathon in Boston. (AP Photo/Robert F. Bukaty)
Ben True celebrates after winning the Boston Marathon 5k in Boston, Saturday, April 18, 2015. The 119th Boston Marathon will be run on Monday. (AP Photo/Michael Dwyer)
HOPKINTON, MA - APRIL 20: Rich Vaillant, of Shrewsbury, gets a nap in under the tent in the Athlete's Village at the starting line in Hopkinton, Mass. before the 119th Boston Marathon. (Photo by Lane Turner/The Boston Globe via Getty Images)
BOSTON, MA - APRIL 20: A banner hangs near the finish line before the start of the running of the 119th Boston Marathon on April 20, 2015 in Boston, Massachusetts. (Photo by Jim Rogash/Getty Images)
Competitors leave the start line in the women's wheelchair division of the Boston Marathon Monday, April 20, 2015 in Hopkinton, Mass. (AP Photo/Stephan Savoia)
HOPKINTON, MA - APRIL 20: Information booth volunteers dance in place to Pharrell Williams' 'Happy' to stay warm, before the starting line in Hopkinton, Mass. Left to right are Tom Regan, wife Judi Regan and Jen Brooks. The 119th Boston Marathon is run on Monday, April 20, 2015. (Photo by Pat Greenhouse/The Boston Globe via Getty Images)
WELLESLEY, MA - APRIL 20: Wellesley College student Maria Castano gets the scream tunnel ready. Getting ready for the the 119th Boston Marathon. (Photo by Suzanne Kreiter/The Boston Globe via Getty Images)
WELLESLEY, MA - APRIL 20: Ashley Wilson, 16, even with a torn ACL, is a volunteer spotter along the route. Getting ready for the the 119th Boston Marathon. (Photo by Suzanne Kreiter/The Boston Globe via Getty Images)
Police flank an explosive ordnance disposal officer, second from left, as they patrol past the site of the first 2013 bombing site before the start of the Boston Marathon Monday, April 20, 2015 in Boston. (AP Photo/Charles Krupa)
Competitors leave the start line in the women's wheelchair division of the Boston Marathon Monday, April 20, 2015 in Hopkinton, Mass. (AP Photo/Stephan Savoia)
Spectators pass through a security checkpoint near the finish line of the Boston Marathon Monday, April 20, 2015 in Boston. (AP Photo/Robert F. Bukaty)
BOSTON, MA - APRIL 20: People have their bags checked at a checkpoint along Commonwealth Avenue as the Boston Marathon prepares to get underway April 20, 2015 in Boston, Massachusetts. This is the 119th running of the Boston Marathon. Photo by Darren McCollester/Getty Images)
Boston Marathon runners wait to board shuttle buses in Boston to the starting line in Hopkinton, Mass., Monday, April 20, 2015. (AP Photo/Robert F. Bukaty)
HOPKINTON, MA - APRIL 20: Men's wheelchair division leave the starting line in Hopkinton, Mass. of the the 119th Boston Marathon. (Photo by Bill Greene/The Boston Globe via Getty Images)
HOPKINTON, MA - APRIL 20: Runners stay warm with foil blankets under a tent at the Athlete's Village at the starting line in Hopkinton, Mass. before the 119th Boston Marathon. (Photo by Lane Turner/The Boston Globe via Getty Images)
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"It's always been a dream of mine to run Boston," said David Harris, 42, of Atlanta.

Open divisions start around noon. In total, about 30,000 people are expected to attempt the course.

Known as a tactical racer with a sprint finish, men's elite headliner Desisa posted a personal best of 2:04:45 in Dubai in 2013. He won Boston in 2:09:17 last year and also won in 2013.

Kenya's Geoffrey Mutai enters the race with the fastest personal time of 2:03:02, a course record he set with his 2011 Boston win. Kenyan Wesley Korir whose personal best is 2:06:13, is returning for the fourth time after having won in 2012.

Meb Keflezighi, who became the first American to win Boston in more than three decades when he scored an emotional victory in 2014 on the anniversary of the bombings, said he would sit out Boston to prepare for the Olympic marathon.

The year that Keflezighi won saw a near-record number of runners and throngs of cheering spectators packing the sidelines and was hailed as a symbol of the city's recovery from the bombing attacks.

The men and women's winners this year will receive $150,000.

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