The song is used to introduce the play, a story about the occurrences in a prison (in real life Mountjoy Prison where Behan
had once been lodged) the day a convict is set to be executed. The triangle in the title refers to the large metal triangle which was beaten daily in Mountjoy Prison to waken the inmates ("The Auld Triangle goes Jingle Jangle"). The triangle still hangs in
the prison at the centre where the wings meet on a metal gate. It is no longer used, though the hammer to beat it is mounted beside it. In the original play by Brendan Behan, the song is written as the "old triangle" not "auld triangle".
The triangle was rung regularly to signify points in the prisons routine.
A second level of meaning is hinted at in the final verse in which the singer imagines himself dwelling
in the women's prison. Another mourns the separation from ''his girl Sal". These hint at the internal erotic fantasies that prisoners use to separate themselves from the harsh prison environment. In this meaning the old triangle becomes the female pudenda
and the Royal Canal the vagina. 
As with many Irish ballads, the lyrics have been changed with
each passing cover. For example, the Dropkick Murphys recording condenses the structure into a three-lyric section song with a chorus based on the last two lines
of each stanza in the original.
Les mer her