Åke Olson

“ But he seems not to have been able to run the mountain line with sufficient accuracy over the summit of the mountain including the northern part of the ring-wall. This indicates that the walls of the Kastro fortifications were already in place when the survey work for the tunnel started. It is obvious that tunnelling in the dark with only oil-lamps for lighting necessitated a method for keeping a straight course. The tunnel follows the straight line into the mountain in a way that one edge of the tunnel touches the straight line and after this turns to the other side. ”

“ The start of the north tunnel achieves a high degree of accuracy; in altitude it is within a few decimetres; the starting point is correct on the lines, also within a few decimetres, but in direction there is a deviation of 0.8 degrees. In length the error is larger–perhaps about 5 m–but this error is less critical. From the situation when starting the north tunnel we can estimate the degree of accuracy possible for Eupalinos. ”

“ The unit presented by Kienast is an average of different measurements between 19.45 m to 21.20.↑ A measuring chain or a rope on the flat floor does not need to be corrected for sag. A certain strain must be applied by hand but no influence of temperature would occur because of the regular conditions. A chain is not influenced by moisture. If the handles of the chain were arranged in a way that they could be fixed to a peg, where the centre of the peg defines the end of the chain, a still higher accuracy could be obtained. ”

“ The straight line was the main component in Eupalinos' approach to the work and all parts of the tunnels follow straight lines. There are no more turning points in the north tunnel than listed above (A – G) .
2. Eupalinos was using measuring units, and I suggest that for angles one unit is equal to 1/12 of a straight angle and for distances one unit is equal to 20.59 m. ”

“ Using the same chain for all measurements in the tunnels increases the accuracy. Accuracy would be lower if a tape made of fibre or leather were used.↑ Grewe analyses a proposed navigation based on a grid where ›compressed‹ distance units along an extension of the north tunnel are projected perpendicular on the actual cut segments: K. Grewe, Licht am Ende des Tunnels. Planung und Trassierung im Antiken Tunnelbau (Mainz am Rhein 1998) 58–69. This theory is based on the irregular positions of the wall marks and not compatible with possible chain-shifts on the floor of the tunnel. ”

“ As Eupalinos unit is 20.59 m this probably represents the length of the chain. As Eupalinos is using a unit of 20.59 m for distance measurements the chain would have had this length. A chain flat on the floor would give an accuracy of a few centimetres per chain length and for a full segment of the tunnel less than 1 m. [15] The measurements would have followed the straight lines forming the tunnel segments as close as possible preferably with the chain lying on the floor. At the shifts of the chain marks would have been painted on or cut in the floor. ”

“ After choosing to turn at A he kept this turning point fixed. When leaving A, he would not yet have been able to decide the position of the next turning point because the condition of the rock was unknown for him. ”