The two-hour plus hard runs are what get the good marathoners through the last third of the race. They don’t get faster; they develop the fortitude not to slow down. Jack Foster (Silver medalist in the Commonwealth Games Marathon in 1974) talks about this in his delightful little monograph entitled The Ancient Marathoner. There was a practice run on the Munich Olympic course and Jack ran in this race. And he talks about the last six miles of the race where he felt he was struggling more and more, but each mile split was the same 5.05 or so that he was looking for. His point being that your head often begins to struggle before your body actually does so you have to fight your psychological doubts. This is the hard part of marathoning and can only be mirrored by doing marathon distance training runs. I think there is a train of thought that once a runner runs say 1:08 for a half they have to get faster to run say 2.20 for a marathon. This is not the case; they now have to get stronger to be able to maintain sub 1:10 half pace for the full marathon.