"Cecilia" is a song by American music duo Simon & Garfunkel, released in April 1970 as the third single from the group's fifth studio album, Bridge over Troubled Water (1970). Written by Paul Simon, the song's origins lie in a late-night party, in which the duo and friends began banging on a piano bench. They recorded the sound with a tape recorder, employing reverb and matching the rhythm created by the machine. Simon later wrote the song's guitar line and lyrics on the subject of an untrustworthy lover. The song's title refers to St. Cecilia, patron saint of music in the Catholic tradition.

The song was a hit single in the United States, peaking at number four on the Billboard Hot 100. On the Cash Box Top 100, it reached number one.

"Cecilia" also did well in Canada, Germany, the Netherlands, and Spain, where it reached number two, and also in Switzerland and Belgium, where it peaked at number three. The song has been the subject of numerous cover versions, most notably by the singer Suggs, whose version featured the ragga duo, Louchie Lou & Michie One and reached number four in the United Kingdom in 1996.

The song's origins lie in a late-night party between the duo and friends. The song's rhythm was developed by Simon, Garfunkel, and Simon's younger brother, Eddie, when the three began banging on a piano bench during the party. They recorded it for fun utilizing a Sony tape recorder and employing reverberation. In doing so, they were able to synchronize their live rhythm with the reverberating sound on the recording. A friend grabbed a guitar, strumming and punctuating the rhythm with "aahs".

...
Wikipedia