A terril is a coal slag heap, and in the old Artois coalfield they punctuate the horizon like unfinished pyramids. This one, numbered 31 in the local inventory of the mining basin, lies on the southern fringe of the field, near Norrent-Fontes and Mametz, where the plain of the Lys starts to tilt against the low hills of Artois. Heaps like this were built up over decades from the waste rock hauled out of the pits, and many are conical, a few are flat-topped and some stretch in long ridges. Left alone, they have turned into oddities of nature, with warm black soil that suits unusual plants, birch scrub, and in summer a surprising number of butterflies.
The ride here is rural and quiet. The country between Lillers, Auchel and Aire-sur-la-Lys is a patchwork of fields, hedgerows and small brick villages, with roads that run in long lines and sudden right-angle turns, a pattern inherited from old field boundaries. The surface is fair, though cobbled stretches and farm mud appear without warning, especially in autumn. Wind can be strong across the open plain, and rain comes in from the Channel, so a waterproof is wise. In spring the fields glow yellow with rapeseed.
Aire-sur-la-Lys, eight kilometres away, has over ten thousand people and is the practical choice for fuel and a meal. Its main square is framed by Flemish-style brick houses, and the belfry, listed by UNESCO along with others in northern France and Belgium, rises over the market place. The cités of the label, the miners' housing estates of the Justice and the Moulin, belong to the former mining villages nearby, with their long rows of identical houses, each with a chimney and a patch of garden.
To climb a terril, check first that it is open, because some are protected nature reserves and others are private. If you can, go up at sunset. The slope is loose, the view is wide, and the whole district spreads out below, with church spires and chimneys catching the last light. It is a landscape made by human hands, but time has given it a certain strange beauty.