Roman road between Zarzalejo and El Escorial

Only a few sections haven't seen the paving stones uprooted and used for building walls and farm buildings. This is one such section. On the ground, this road is not at all a straight line. From the air and on the map it is a typical straight Roman road!
The red and white waymark is for the GR10, the long distance walk from Valencia to Lisbon - or Lisbon to Valencia if you prefer. This is recent. I was surprised to see it here as previously, the GR10 passed many kilometres further north, through the centre of the Sierra de La Guadarrama. Perhaps they will be alternating the routes every couple of decades or so in order to give the paths a rest!
If so, it is a good idea (although I am told that the GR10 is not much used and I must say that on my many walks using fragments of the GR10, I have never seen any long-distance walkers!)