The violence by bandit groups was so bad when he was young that his parents sent him to live with his grandmother in the nearby city of Valledupar, near the Venezuelan border. He returned at age 16 with a high school degree and got a job teaching reading to schoolchildren.

By the time he was in his 20s, Colombia’s long internal war had drawn paramilitary bands to the lawless marshlands and hills surrounding La Gloria, leading to clashes with guerrillas and intimidation of the local population by both groups.

Into that violence, which has since ebbed, Mr. Soriano ventured with his donkeys, taking with him a few reading textbooks, encyclopedia volumes and novels from his small personal library. At stops along the way, children still await the teacher in groups, to hear him read from the books he brings before they can borrow them.

A breakthrough came several years ago when he heard excerpts over the radio of a novel, “The Ballad of Maria Abdala,” by Juan Gossaín, a Colombian journalist and writer. Mr. Soriano wrote a letter to the author, asking him to lend a copy of the book to the Biblioburro.

After Mr. Gossaín broadcast details of Mr. Soriano’s project on his radio program, book donations poured in from throughout Colombia. A local financial institution, Cajamag, provided some financing for the construction of a small library next to his home, but the project remains only half-finished for lack of funds.

There is little money left over for such luxuries on his teacher’s salary of $350 a month. Already the family’s budget is so tight that he and his wife, Diana, opened a small restaurant, La Cosa Política, two years ago to help make ends meet.