BOSTON (Reuters) - Ethiopia's Lemi Berhanu Hayle and Atsede Baysa will line up among the world's top distance runners on Monday to defend their Boston Marathon titles, with tens of thousands of spectators expected to line the course amid tight security.

Men's champion Hayle won the 2016 marathon in a tactical 2 hours, 12 minutes and 44 seconds, while women's title holder Baysa won in 2:29:19.