The new leaves on the plane trees along the Canal St Martin filter the morning sunlight but don’t yet cast heavy shade.  Beyond the lock the canal dives underground, to emerge 2km downstream at Port de l’Arsenal.   Square Frédérick Lemaitre spans the mouth of the tunnel, offering a strangely flowery perspective along the waterway.

The Canal St Martin, linking the Seine and the Canal de l’Ourc, was inaugurated by Charles X in 1825.  Forty years later Baron Haussmann decided that the section of the canal approaching Place de la Bastille should be covered over, to allow the development of a series of squares along the new Boulevard Richard Lenoir.   Roof lights in the squares allow daylight to illuminate the brick vaulted tunnel beneath them.