A lock is a stretch of river water enclosed by gates, built to raise or lower boats from one water level to another. Flatford Lock was one of thirteen locks along the River Stour. Constable’s father, Golding Constable, was one of the commissioners of River Stour Navigation, which was responsible for keeping the locks in order.

During the 1820s, Constable made several paintings of Flatford Lock – one of his favourite haunts. His first paintings of the subject had a vertical format. In 1826, he converted the vertical composition into a horizontal one, extending the scene to the right and varying the action.

The paintings were big canvases – ‘set pieces’ destined for exhibition at the Royal Academy. A boat passing a lock, 1826, was commissioned privately but became the artist’s diploma work when he was elected a Royal Academician in 1829.

In such large canvases, Constable was faced with complex compositional problems to resolve. He moved things around in the landscape – trees, figures, gates – to make the composition work.