The earliest evidence of 'tangos' being sung on stage in Buenos Aires comes from the mid Nineteenth Century (though if we could hear them today, we probably wouldn't recognise them as what we would call Tango). Tango bands at that time would often be made up of flute, violin and guitar, or tangos might be played on a solo piano in the brothels and cabarets.
The oldest tango which is still in the repertoire of Tango orchestras was written by Rosendo Mendizabal, a pianist working in a club, and was named, after one of their regular clients who came from the province called Entre Rios, El Entrerriano. The tango was written in the 1890s.