Hardest marathon courses

Total climbing on its own is a poor answer to "which marathon is hardest". Boston climbs less than most of the field and still ruins more races than courses twice as hilly, because a long net descent loads the quadriceps eccentrically and that damage arrives in the last 10 km. Mexico City barely climbs by Alpine standards and sits at 2,250 m, where the air does the work instead. The rating here prices all three: total ascent, the descent in excess of it, and course altitude above 1,500 m. Courses sharing a rating are ordered by total ascent, and the rating stays editorial — where local knowledge beats the elevation profile, it wins. That is why Rome carries far more listed ascent than its rating suggests: its elevation still comes from a surface model, which returns rooftops rather than ground in a dense city and inflates the climbing figure, so the rating reflects the course as run instead.