Sentinels was written for the Brodsky Quartet and John Metcalfe. An unusual feature of the Brodskys' performances is that with the exception of the 'cellist, they play standing up; Butler imagined the four standing players to be acting as sentries, standing guard, keeping watch over the seated 'cellist - hence the title. A friend pointed him in the direction of the opening scene of Hamlet - with its sentries, its sinister and slightly surreal atmosphere, its ghost, its uncertainty and apprehensiveness - and the flavour of the piece was fixed. The piece is really a long, unrelenting march whose pulse never slackens or quickens, and in which slightly quirky military-style gestures are almost always present. Sentinels was written for the Brodsky Quartet and John Metcalfe and first performed by the Brodsky Quartet and John Metcalfe (viola) on 23 May 2006, at the Royal Pavilion, Brighton.