On September 23rd we did a study trip, starting at the Jinshanling section of the Great Wall, and walking to Simatai. For the first part of the hike we were accompanied by an expert from the China Great Wall Conservation Association, who provided information as we walked.
Some key points: the orange-coloured bricks are from the original Ming Dynasty construction, the grey-coloured bricks are from the 1986 reconstruction; in several places there are secondary walls that were constructed to make it more difficult for horseriders to get close; throughout the Jinshanling section the towers are spaced 50-200m apart; there was not enough money to reconstruct all of the two-level towers - you can see where those were by checking for the round foundations for the wooden pillars that held up the roofs.
Statistics: 3 hours hiking over 9.6km at approx. 3km/hr (5 hours total time ... hey, we were listening to the expert!); start height 277m, highest point 607m, approx. 710m going up, 745m going down. Estimated 2047kCal burned.