A stretch of water, a plain as far as the eye can see, a very parallel fold: the horizontal line is soothing. It anchors us, brings us down to earth, and unlike its vertical cousin, which points towards the summits and the unknown, there is something reassuring about it. Artists have always used it, sometimes to define the horizon, sometimes to elongate an odalisque, but always in the spirit of establishing a base, of not letting the subject float. Take a look at the works in this week's selection, and put things straight!