section here,’ he gestured at a cluster of grey strings in the first section of the khipu, ‘corresponds to the highlands along the Inca Trail leading to Machu Picchu. By going back towards Cuzco, we found that other colours match particular features of the landscape.’ He gently nudged one of the strands with a toothpick. ‘This shade of turquoise seems to represent river valleys, for example.’
Eddie took a closer look. The string had multiple knots of different types along its length. ‘So the map tells you what landmarks to look for, the colours of the strings show you the terrain . . . so the knots are, what? Directions? Distances?’
‘Both, in a way,’ said Nina.
‘The Incas had a system of sacred routes radiating outwards from Cuzco,’ Osterhagen explained. ‘They were called ceque pathways, and they connected all corners of the empire. Some were actual roads or paths, but most were just straight lines from one huaca to another. We knew that the pathways had ritual significance – the most important ones, the forty-one ceques around Cuzco, can be linked to the lunar calendar. But nobody has ever worked out how to connect all the others around the empire.’
‘Until now, at a guess,’ Eddie said, seeing that Nina was practically bouncing in her seat with excitement.
‘You got that right,’ she told him with a broad grin. ‘Leonard used the data he got by backtracking from Machu Picchu to Cuzco to figure out that the knots closest to the main cord give you directions, based on star charts – the Incas had a very advanced astronomical system.’
‘Not as good as the Egyptian one, though,’ Macy chipped in, defending the non-Cuban half of her heritage.
‘Maybe not, but still accurate enough to be usable for navigation. So that’s part of the key. And the other part is also on the khipu – the rest of the knots. The Inca numerical system was decimal, like ours, and on a khipu it worked like an abacus. The knots represent units, tens, hundreds and so on, depending on their position. If you know the system, you can tell what number’s recorded on a piece of string at a glance, or even by touch.’
‘Again, because I had reference points,’ said Osterhagen, ‘we were able to work out what the numbers meant. They are indeed distances. Nina calculated how they relate to huacas in the real world. In her head,’ he added, impressed.
‘So you know the total distance they travelled?’ asked Kit.
‘Something like seventeen hundred miles,’ Nina replied.
‘Jesus,’ said Eddie. ‘And you said it was a thousand miles in a straight line? Seven hundred miles is a hell of a detour.’
‘It’s because they were sticking to what they knew for most of it,’ Macy said. She opened up a large map of South America. ‘From Cuzco, they were pretty much heading northwest along the east side of the Andes. I guess they didn’t want to go into the jungle.’
‘But they had to eventually,’ added Nina. She pointed back at the section of the khipu where the coloured threads became predominantly green and blue. ‘We think the green ones represent jungle terrain. And the directions at the top of each string almost all indicate northeast. The blue ones, it seems likely that they mean to follow rivers.’
‘Makes sense,’ said Eddie. ‘Not a lot of other landmarks in the jungle.’
‘Especially if you’re used to living amongst mountains.’ She moved her finger back along the khipu. ‘So if we backtrack from Paititi, they covered long distances with comparatively few changes of direction . . . and then here’ – she indicated the point where the colour scheme reverted to the redder end of the spectrum – ‘is where they crossed from the Andes into the Amazon basin. But even up in the highlands, they were still heading mainly northeast . . . until here.’
Eddie examined the strings she was pointing out. The exact meaning of the knots at their tops were a mystery to him, but he immediately saw what she meant: those to the right of her finger were tied right over left, while on the other side they were fastened left over right. ‘So that’s where they changed direction,’ he deduced. ‘They stopped following the Andes and went out into the jungle.’
Nina nodded. ‘That’s the dogleg, where the extra seven hundred miles came from. And it’s something else too.’
He could tell from her struggle to contain another smile that it was something big. Which, considering what they were looking for,