Who roamed ancient Roman roadsides waiting for unwary travelers during the medievel period?
robbers, highwaymen, vagabonds
http://en.wikipedia.org/wiki/Highwayman
Sometimes they were ex-knights whose lords had been put out of commission in some way. This type of thing occurred in medieval Japanese society, too, when samurai were suddenly "at loose ends" if their lord were killed or captured or whatever. These robbers were called ronin.
Would some of these people be runaway slaves or serfs?
Yes, they could be runaway serfs or slaves.
During the medieval period, the individuals who roamed ancient Roman roadsides waiting for unwary travelers were known as highwaymen or bandits. These outlaws were common throughout Europe and sought to ambush and rob unsuspecting travelers, often taking advantage of the isolated and poorly protected roadways of that time.
To find this answer, you can start by conducting a search using a search engine or referring to historical sources related to the medieval period. Keywords such as "highwaymen," "bandits," "medieval Europe," and "Roman roads" would be helpful to narrow down the search. Consulting reliable historical books, articles, or academic sources on the topic can provide you with more detailed information on the subject.