The Dayton Marcos were a Negro League baseball team that is now defunct along with the Negro League. They were based from Dayton, Ohio.
The Dayton Marcos history does go back farther than the Negro League though. As an independent team and also in the Ohio-Indiana League, they played black and white teams all over the country throughout the 1910s.
According to the Negro League Baseball Players Association Website, old newspaper accounts and fading memories are the only sources of information on the Marcos  even as they burst into the Negro League. They played in the then newly formed Negro National League, which was formed by Rube Foster. The Marcos were one of those first eight teams to play in the first Negro League to survive a full season.
During this time, the Marcos did play against some heavy competition, including that of Satchel Paige.
Dayton left the league after one year and a last place finish, and played independently until the mid 20s. They then rejoined briefly for part of 1925, when they finished in second-to-last and left the league once again. Although, they were a significant part of Dayton sports history, too little is known about them to factor them in too highly.
The Marcos survived until the Second World War. Dayton did not have a baseball team again until 2000 when the Dayton Dragons formed.