He goes further. Aumance was one of around 75 places once known by the name Equoranda, a word with an unknown root that resembles the Greek and Gaulish for “sound-line” or “call-line”. All the Equoranda settlements Robb visits turn out to be on low ridges or shallow valleys, and would, he writes, “have made excellent listening posts”. Examined in this light, one word in Caesar’s account becomes fruitful: he observes that the Gauls “transmit the news by shouting across fields and regios”, a word that can be translated as “boundaries”. An ancient Persian technique for acoustic surveying, still current in the 19th-century south of France, involves three men calling to one another and plotting their position along the direction of the sound. Put the pieces together and you end up – or Robb does – with “the scattered remains of a magnificent network” that could have acted not just as a telegraph system but as a means to map the Druids’ boundaries on to the earth.