I was used to diagrams and drawings, but this was a drawing of nothing I could recognise. The writing was in Latin, and I saw the words Aethiopia and Fortunate Islands, and then right out in a corner, Britannia. The lines seem to be scrawled everywhere, and all over the picture were trails of mounds drawn in, like a field where moles have been at work.

“Those, are they mountains?”

“Yes.”

“Then it’s a picture of the world?”

“A map.”

I had never seen a map before. At first I could not see how it worked, but in a while, as he talked, I saw how the world lay there as a bird sees it, with roads and rivers like the radials of a spider’s web, or the guide lines that lead the bee into the flower. As a man finds a stream he knows, and follows it through the wild moors, so, with a map, it is possible to ride from Rome to Massilia, or London to Caerleon, without once asking the way or looking for the milestones. This art was discovered by the Greek Anaximander, though some say the Egyptians knew it first. The map that Galapas showed me was a copy from a book by Ptolemy of Alexandria. After he had explained, and we had studied the map together, he bade me get out my tablet and make a map for myself, of my own country.

When I had done he looked at it. “This is the centre, what is it?”

“Maridunum,” I said in surprise. “See, there is the bridge, and the river, and this is the road through the market place, and the barrack gates are here.”

“I see that. I did not say your town, Merlin, I said your country.”

“The whole of Wales? How do I know what lies north of the hills? I’ve never been further than this.”

“I will show you.”

He put aside the tablet, and taking a sharp stick, began to draw in the dust, explaining as he did so. What he drew for me was a map shaped like a big triangle, not Wales only, but the whole of Britain, even the wild land beyond the Wall where the savages live. He showed me the mountains and rivers and roads and towns, London and Calleva and the places that cluster thick in the south, to the towns and fortresses at the ends of the web of roads, Segontium and Caerleon and Eboracum and the towns along the Wall itself. He spoke as if it were all one country, though I could have told him the names of the kings of a dozen places that he mentioned. I only remember this because of what came after.