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The construction of Xerxes' bridge over the Hellespont*

Published online by Cambridge University Press:  23 February 2012

N.G.L. Hammond  and
L.J. Roseman
N.G.L. Hammond
Affiliation:
Clare College, Cambridge
L.J. Roseman
Affiliation:
University of Washington, Seattle
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Extract

The bridging of the Hellespont by Xerxes was a unique achievement. How was it done? The Chorus of Elders in Aeschylus' Persians expressed their wonder at ‘the flax-bound raft’, and Herodotus described the construction of the two bridges, each with warships as pontoons, with cables well over a kilometre long, and with a roadway capable of carrying a huge army. Classical scholars have generally found these accounts inadequate and even inexplicable, especially in regard to the relationship between the pontoons and the cables. The Hellespont has strong currents which vary in their direction, turbulent and often stormy waters, and exposure to violent winds, blowing sometimes from the Black Sea and sometimes from the Mediterranean. How were the warships moored in order to face the currents and withstand the gales? Did the warships form a continuous platform, or was each ship free to move in response to weather conditions? What was the function of the enormous cables? How and where were they made? Did they bind the pontoons together? Did they carry the roadway? How were they fixed at the landward ends? This article attempts an answer to these questions through the collaboration of a classical scholar and a mechanical engineer.

Type
Articles
Information
The Journal of Hellenic Studies , Volume 116 , November 1996 , pp. 88 - 107
Copyright
Copyright © The Society for the Promotion of Hellenic Studies 1996

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References

1 The words and resume and They are not dependent on and on as Grote, Rawlinson and Macan suggested (H. and W. ii 142); for that interpretation would reqire a different order of words and there is no sense in the proposed translation ‘at right angles to the Black Sea.’ See Myres 222, who translated as I do. Hill, D., A history of engineering in classical antiquity (London 1984) 65Google Scholar followed Rawlinson.

2 The subject of is uncertain. H. and W. ii 143 supposed it was ‘the bridge (i.e. here the moored ships)’, but they had just said that ‘Herodotus regarded the cables with the roadway as the true bridge.’ I suppose that Herodotus had Xerxes' engineer in mind as the personal subject.

3 See the apparatus criticus of the Oxford Classical text for suggested emendations. Since begin with the same three letters, one word could easily be omitted by a scribe. There are no paleographical grounds for emending to (H. and W. ad loc.)

4 The importance of providing more than one bridge, for instance at the Hellespont, was appreciated by Maurice 224–5. But H. and W. ii 169 wrote of ‘the bridge’ despite the plural word at vii 25.1 and vii 114–5.

5 Maurice, taking Abydus to mean ‘Abydus city’, carried the bridges from the city over to the coast not of Sestus but of Madytus, reckoned the length of each bridge there as 4,220 yards, and exposed both bridges to changing currents (217). For the site of Abydus city, see Cook, J.M., The Troad (Oxford 1973) 56.Google Scholar

6 Macedonia, Thrace and Illyria (Oxford 1926).

7 Maurice, who seems to have been unaware of Stanley Casson's work, proposed an inland route on his map (218). The huge army certainly used more than one route (pace Casson and Maurice) in the Chersonese as in Thrace (see CAH iv 537–9), and not just the one route even for a ‘double column, one of troops and one of transport’ (Maurice 224).

8 Maurice's location for the bridges made the distance to the other coast 4,220 yards, which is vastly more than seven stades (217). In making the stade 185 m. I follow Brunt, P.A., Anabasis Alexandri i (Harvard 1976) 488.Google Scholar

9 For this calculation see Hammond's, summary in Ancient World xxv (1994) 23–4.Google Scholar

10 See (n. 1) above.

11 See H. and W. ii 143, whereas Maurice did not consider the currents in his siting of the bridges (216–7 with fig. 1).

12 Thus corn-barges, running downstream, would have used a central opening in the bridges where the current ran fast, whereas the light craft, going up the Hellespont, would have used openings near the coast and taken advantage of the counter currents.

13 Burn 320 judged the cables to be continuous and so ‘about a mile long’, and he reckoned that the heavier kind of cable would have weighed ‘close on 100 tons’.

14 Herodotus vii 55.1 reported that the armed forces and Xerxes himself crossed on the eastern bridge, while the draught animals and the retainers crossed on the western bridge. If the camels crossed on the latter bridge, the palisade would have been high to prevent them seeing the water. On the other hand they might have been transported by ships, for the fleet was also available.

15 This would allow for a column of four armed men abreast and of two cavalrymen abreast. Maurice thought of ‘a column of troops in fours’ at narrow places on the route, of which the bridge-roadways are examples. It is thus credible that the crossing of the two bridges did take a week, day and night.

16 Basic articles in the Encyclopaedia Britannica 1957 and 1993 describe a process which is entirely compatible with Herodotus' account. Both show that ‘capstans’ (‘donkeys’) are used in several phases of the manufacturing process: ‘Friction on the revolving capstans draws the yarn through the machine’ (1957, xix 546). ‘Strands also known as readies are formed by twisting yarns…together’ (1993, x 176). Three or more strands are twisted (laid) into a rope (the 1993 edition is more apt to use the word ‘flyer’ than capstan). ‘The three subassemblies of the rope-laying machine arranged in tandem horizontally, are the foreturn flyers (rotating strand bobbins), the capstan flyer (pulling mechanism), and the receiving flyer (rope-twisting and storage bobbin mechanism)’ (1993, x 176). Instead of winding the rope ‘onto a heavy steel bobbin’, the floating ‘raft’ was used as a ‘ropewalk’ (before removing any ships to make the gaps described in Herodotus) over which the rope was laid in situ and the final capstan was on land. It should be noted that any twisting of a finished cable or rope will either create kinks or unlay (unwind) the strands of the rope. Therefore, the words of Herodotus cannot be describing what was done to the finished cables.

17 Chapman, Robert (formerly foreman to Mssrs. Huddart & Co., Limehouse; and Master Ropemaker of H.M. Dockyard, Deptford), A treatise on ropemaking as practiced in private and public ropeyards, with a description of the manufacture, rules, tables of weights, etc., adapted to the trade, shipping, mining, railways, builders, &c., (Philadelphia 1869) 22.Google Scholar

18 Casson, 54.

19 Landels, J.G., Engineering in the ancient world (London 1978) 145, fig. 52.Google Scholar

20 Chapman, 103.

21 Kutz, fig. 16.9.

22 Chapman (n. 17) 6: ‘This work has been written with the view of assisting the workman in obtaining a knowledge of the calculations necessary to the art of ropemaking; having in the course of my own practical employment, been frequently in want of such rules, and as often been disappointed when asking information of those it might have been expected from, I was in consequence, compelled to form rules to enable me to carry on the work and to answer questions put to me by the officers of the dockyards through the Lords of the Admiralty, and which were often very absurd; hence, the following rules and tables will be found chiefly to consist of those practical rules connected with the art of ropemaking.’

23 Chapman (n. 17), 29–30.

24 Chapman (n. 17), 31.

25 Holdworth, Richard and Lavery, Brian, The ropery visitor handbook (Chatham [Kent] 1991) 12.Google Scholar

26 Kutz, table 16.75.

27 Morrison, J.S. and Coates, J.F., The Athenian trireme (Cambridge 1986) 180.Google Scholar

28 Baker, Ira Osborn, A treatise on roads and pavements (New York 1908) 274Google Scholar: ‘Plank roads were once somewhat common in the heavily timbered portion of the northern United States and of Canada. The first plank road on the continent was built in Canada in 1836 … The method of construction most commonly followed is to lay down lengthwise of the road, two parallel rows of plank called sleepers or stringers, about 5 ft. apart between centers, and upon these to lay cross-planks 3 to 4 in. thick and 8 ft. long … The planks were often covered with gravel, sand, or loam to protect them from wear. … when kept in repair, plank roads make a comparatively smooth roadway possessing some advantages for both heavy and light traffic…’

29 I” dia. approximately 3” cir. Breaking strength = 4,032 lbs. (per Chapman [n. 17]). Total breaking strength per joint = = 12,000 lbs.

30 Chapman, 197.

31 Marks standard handbook for mechanical engineers 9 (New York 1987), table 5.1.1

32 Civil engineer's reference book 4 (London 1989), table 31.6 ‘Timber properties’.

33 Lange, N.A., ed. Handbook of chemistry6 (Sandusky, Ohio 1946) 1356.Google Scholar

34 Coates, J.F., Platis, S.K., and Shaw, J.J., The trireme trials, 1988 (Oxford 1990) 52Google Scholar describes advanced oar design weighing 4.6 kg. This figure is used both for the penteconter and the trireme oars.

35 Casson, 250.

36 Casson, 250.

37 If the roadway cables are attached to the boats (which they are not), the end restraint concept would be an inefficient manner to react what would then be additional tension in these cables. Perhaps they were attached in the first design of Herodotus vii 34 in which ‘all’ was lost. But they were not attached in the second design of Herodotus vii 36 so that the cables were still there in Herodotus ix 114. This allowed Oeobazus to have cable (at least pieces) to carry to Sestus.

38 In a suspension bridge, half of the dead weight (2,048,000 lbs.), plus half of the live load (1,150,000 lbs.) would be supported (i.e., reacted) at each end. Since the present reconstruction allows for only 202,000 lbs. of allowable working load at each end, this is clearly not a suspension bridge.

39 We owe a special debt of gratitude to Professor Carol Thomas, whose enthusiastic interest and helpful comments have been an inspiration.