For a long time after the Olympic marathon started, there were no long-distance races, such as the marathon, for women. Although a few women, such as Stamata Revithi in 1896, had run the marathon distance, they were not included in any official results. Marie-Louise Ledru has been credited as the first woman to complete a marathon, in 1918. Violet Piercy has been credited as the first woman to be officially timed in a marathon, in 1926.

Arlene Pieper became the first woman to officially finish a marathon in the United States when she completed the Pikes Peak Marathon in Manitou Springs, Colorado, in 1959. Kathrine Switzer was the first woman to run the Boston Marathon "officially" (with a number), in 1967. However, Switzer's entry, which was accepted through an "oversight" in the screening process, was in "flagrant violation of the rules", and she was treated as an interloper once the error was discovered. Bobbi Gibb had completed the Boston race unofficially the previous year (1966), and was later recognized by the race organizers as the women's winner for that year, as well as 1967 and 1968.
What marathon did the first woman officially finish, based on the paragraph.
The first marathon that a woman officially finished was the Pikes Peak Marathon, completed by Arlene Pieper in 1959.