Tropis X: Διεθνές Συμπόσιο για την Ναυπηγική στην Αρχαιότητα (Ύδρα 2008)

 

Το Tropis (από την αρχαία Ελληνική λέξη τρόπις, «καρίνα πλοίου») είναι μια σειρά πρακτικών συνεδρίων για την Αρχαία Ναυπηγική.

Τα συμπόσια διοργανώνονταν κατά διαστήματα από το 1985 έως το 2008 από το Ελληνικό Ινστιτούτο για τη Διατήρηση της Ναυτικής Παράδοσης και στα οποία συμμετείχαν διεθνείς υποβρύχιοι αρχαιολόγοι, κλασικοί αρχαιολόγοι και άλλοι μελετητές. Το Tropis επιμελείται ο Χάρης Τζάλας, πρόεδρος του Ινστιτούτου, και χρηματοδοτείται εν μέρει από το Ελληνικό Υπουργείο Πολιτισμού.

Παρατίθεται, στην Αγγλική γλώσσα (γλώσσα συνεδρίου), το πρώτο μέρος της Εισήγησης μου στο άνω διεθνές Συνέδριο, στην Ύδρα το 2008, με θέμα “Ο Δίολκος στον Ισθμό της Κορίνθου”:

«Introduction

The Diolkos was a paved roadway connecting the Corinthian Gulf with the Saronic Gulf. It was constructed during the rule of the Kypselid dynasty, probably in the seventh century B.C. The Kypselids originally planned to cut a canal across the Isthmus in order to create a navigable waterway between the two gulfs, thereby facilitating maritime traffic and eliminating the hazardous voyage around the southern Peloponnese. This ambitious undertaking, however, proved impracticable. Instead, the Corinthians constructed the Diolkos, an overland paved route designed for the transport of ships and cargoes across the Isthmus. Only part of the Diolkos has so far been excavated. A section approximately 120 m long lies on the Peloponnesian side of the modern Corinth Canal. This stretch is situated north of the road connecting Corinth and Loutraki. A further section, about 50 m in length, is located on the southern side of the same road. Another portion of the paved roadway has been excavated within the grounds of the Army School of Engineers, on the opposite side of the canal. The excavated sections together amount to approximately 1,100 m. Ships, together with their cargoes, were hauled across the Isthmus on wheeled transport vehicles moving along the paved track. The width of the Diolkos varies between 3.5 and 5.0 m, while its total estimated length was approximately 7 km. It was constructed of carefully cut limestone blocks of varying dimensions. The western terminus of the Diolkos, on the Corinthian Gulf, is preserved in situ. The eastern terminus, on the Saronic Gulf, has not yet been identified. Along its entire course, the gradient did not exceed approximately 1–1.5%, thereby ensuring the relatively easy transport of ships and their cargoes. Unfortunately, the precise route of much of the Diolkos remains unknown. Nevertheless, its general course can be estimated. It is evident, for example, that the roadway could not have crossed the Hexamilion Wall. Although this fortification was erected during the fifth century A.D.—many centuries after the construction of the Diolkos—it was built while the latter was still in operation. The Diolkos remained in use for many centuries. The latest references to its operation are found in the works of the Byzantine historians George Sphrantzes, John Zonaras, and John Skylitzes. According to these sources, in A.D. 883 a fleet of one hundred dromons was transported across the Isthmus from the Saronic Gulf to the Corinthian Gulf in a single night. This remarkable operation was celebrated by the Byzantine chroniclers as an extraordinary engineering achievement. It is reasonable to conclude that the Diolkos continued to function until at least the twelfth century, when it was probably destroyed during the Norman invasions. It should be emphasized that the Diolkos formed part of a unified transportation system designed to complement the two principal harbours of ancient Corinth, Lechaion on the Corinthian Gulf and Kenchreai on the Saronic Gulf.

 Observations on the geometry of the construction of the Diolkos

The Diolkos is, in essence, a road that connects two points and runs between two gulfs. The possible routes that link these points are many. Some of these, however, can be excluded on the basis of certain concrete specifications. Thus we shall examine the known surviving sections of the Diolkos so as to arrive at some conclusions regarding its route.

The longitudinal inclination of the existing part of the Diolkos is equal to or less than 1%. It would be desirable for this to be absolutely level, at least over large parts of its course. The Diolkos follows the relief of the ground surface. No artificial constructions can be seen, nor any sharp changes in ground relief, whether built-up areas or depressions.

From the still-existing course of the Diolkos and its longitudinal slope, which is about 1%, it follows that the longitudinal inclination was the characteristic governing and determined its route. Thus its course could not possibly have been along the present canal, because it would then have followed the natural ground relief, with slopes in some areas exceeding 5% and perhaps even reaching 10%. This would have prevented the transport of loads and ships on carriage-trucks over the Diolkos.

 Engineering works

Engineering projects on a very large scale must be excluded.  But there could have been bridges over the stream gullies, which abound in the area of Isthmia.  Parts of the Diolkos would have been built on top of these.

Such engineering projects must have included measures to ensure the drainage of water.  Since the ground in the Isthmus area is basically sandy, the run off and drainage of water could have been provided for easily, without many special works.

Shaping the Ground Surface

The modifications of the surface were, perhaps on a limited scale.  They would probably have amounted to leveling of the ground and, where needed, special changes to ensure runoff of the surface waters.  Large earthworks filling in the gullies in order to provide level continuation of the Diolkos’ route must be excluded.  Instead, there would have been deviations of the Diolkos’ course so as to avoid bridging and filling operations.

As a result, the route chosen would have entailed many engineering works or great modifications of the natural relief.  We must not exclude the building of reinforcing walls of paving blocks.  This would have ensured propping up of the Diolkos’ surface.  They would have been built as a maintenance measure.  According to the archaeologist Ms. Chrys. Kardara, the “Pelesgian” wall in the Isthmia area which the archeologist O. Broneer dated to Mycenaean time, was probably a supporting wall propping up a road.  This indicates early building of retaining walls during the Mycenaean period.

It is logical to suppose that the route of the Diolkos would have avoided the steepest and deepest gullies in the Isthmia area.

 Stations for Servicing Carriages and General Maintenance

The conjectured length of the Diolkos approaches about 7km. Hence it seems likely that there would have been one or more stations: points for servicing the carriages.  Moreover the movement would have been in both directions, and so the carriages would have passed each other.  There must, therefore, have been a secondary shunting or doubling track where the carriages waited, connected to the main line at particular exit and entry points. At the center of the Isthmus, where the terrain is almost flat and at a height of approximately 90,0m. above sea level, we have created by passes on either side of the Diolkos - built exactly like the Diolkos - where one olkos or group of olkoi can exit the main road and wait until traffic from the other direction has passed. If the wait is an extended one, animals may be unloaded to stretch their legs and accommodate their needs alongside the Diolkos.

So, by using the Diolkos simultaneously in both directions transport time for cargo and ships is significantly reduced and more ships per day can be transported.

Ruts, grooves, furrows-made by the movements of the carriages and the waiting ruts would have been worn into the upper surfaces of the paving blocks, exactly the same way as the doubling or shunting tracks of today’s single-track railways. Such an arrangement of shunting tracks has been found in quite a few ancient roads, such as the Sacred-Way in Athens near Reitous, on the Athens-Piraeus road near the Pnyx and between the Long Walls of Athens.

The movements along the Diolkos would probably have been monitored and controlled by means of visual signals or in some other way. Moreover the two Gulfs were both visible from the middle of the Isthmus. It is logical to suppose that the double or waiting line would have been located here. This is also consistent with the horizontal parts of the longitudinal section having a maximal inclination of 3%.

The carriages would have been pulled over the Diolkos by draft animals. As for the warships, for reasons of safety and speed, their movement would have been entrusted to their crews. The movement of the carriages over the Diolkos moreover implies the existence of service stations for supplying food and water.  It should be noted that in ancient times the hooves of animals were not protected by metal shoes. This is why no hoof marks of the beasts of burden have been found on the paving blocks.

On the part of the Diolkos within the grounds of the Engineering School, one can see two wheel ruts (grooves) of different widths, which run along the same line.  This shows that in the more difficult parts of the Diolkos’ route, grooves were carved directly from the beginning into the paving blocks, indicating that a particular route of the carriages was compulsory here.  It seems reasonable that the terrain had been modified, alongside and parallel to the Diolkos, so as to be passable for people and animals, when the carriages were to be drawn.  In addition, there would have been the necessary mechanisms for pulling the carriage trucks around curves and over difficult places.  Here the carriages would have been tied with cables to capstans. Traces of these rope cables can be discerned on the upper layer of parring blocks as a result of the high tension of the pulling and the constant use.

 Materials for Building Diolkos

If we accept a mean width of the Diolkos of 5.0m, its total surface area would have been: 5 x 7000m = 35000m2, taking 7000m as its accepted length.

In addition, if we suppose that an average paving block has the dimentions of 0.60 x 1.5m, its top surface area will be 0.90m2.  The number of paving blocks required would have been 30,000:0.9 = 40,000 blocks.

The total volume of rock required for making the paving blocks is 40,000 x 0.5 = 20,000m3, if the blocks have dimensions of 0.6 x 1.5 x 0.5m, their volume being V = 0.50 m3.

These 40,000 paving blocks include not only the flat pavement of the Diolkos and its local reinforcements, but also its lateral supports and its two-directional slipway ramps.

All this building material would have been quite hard to be transported and distributed along the length of the Diolkos.  To facilitate the work, therefore, there must have been local quarry points for extracting the necessary stone.  Such quarries have been found between the present settlement of O.E.K. and the canal, at the site of Poseidonia, together with the remains of houses dating from the 5th century B.C.  Those installations would logically have belonged to persons who served the Diolkos workers in the quarries.  It should be noted that the whole area of the Isthmus has an abundance of calcareous bedrock in elevations above the surface and extending a few meters below it.  It would have been easy to quarry the building material here for such points, without any elaborate quarry organsition.

 Methods Ways of Building Diolkos

The Diolkos may have been built in more than one section at a time, with work proceeding simultaneously on many fronts.  Naturally, local corrections would have been imposed on the initial overall plan. At first, modification of the terrain to provide the required longitudinal inclination as well as the transverse slope and the level base for the Diolkos. Its exposed surviving parts indicate that the paving blocks were seated in place directly on the natural ground surface, without preliminary formation of an substrate.  Because of the nature of the ground (calcarenite), the paving blocks were roughly worked so that their naturally contacting surfaces were undressed, without anathyrosis.  It would seem that no cement was placed over the surfaces between blocks and the empty spaces between them were filled with sand grains.  With the passage of time, the filtering rainwater created a kind of adhesive substance between the blocks.

 Repairs to the Diolkos

From its exposed and known parts, we cannot be sure whether these were repaired at any time.

On the contrary, it seems that the entire Diolkos is a single structure built within a single period.

Yet it seems logical that there must have been repairs and more general maintenance done to the Diolkos, and that these would both have guaranteed its continuing use.

It must still be ascertained whether during the time of the Diolkos’ use, there were any changes in its route or whether it remained as it was when first built in the epoch of Periander.  There would clearly have been systematic maintenance and the mechanisms for serving it would have been easy and simple.

Moreover the existence, in difficult parts of the route, of lateral reinforcements, as on the part of the Diolkos toward the Corinthian Gulfand the superimposed paving blockson the existing platform surface, to protect the movement of the carriages over curved parts of the route, show that the engineers of the Diolkos had clearly understood the proper geometry of its design and construction, which made for smooth transport of loads and vehicles.

 The known part of the Diolkos is about 1100 meters long.  Hypsometrically it rises from +0 (sea level) up to the north point at the end of the Engineering School’s grounds, which today has a present elevation of +12m.  The inclination of this part of the Diolkos’ route is about 1%.  After the north point, the ground surface rises with a fairly steep slope.  It seems logical that the route of the Diolkoscontinued  thence toward the Peloponnese, which here has a gentler relief.

In the known section, maintaining the inclination of 1% requires a corresponding route made up of interconnected curves.  The part found within the Engineering School has a radius of curvature R = 480.45 and a length of about 200m. This has two special characteristics.

On top of the Diolkos platform have been set two additional rows of building blocks spaced at a distance of about 70cm between them and having a total length of about 30m.

Wherever these added rows of blocks are present, there are no wheel ruts worn into the pavement.

The added paving blocks bear grooves, which are probably traces of the ropes which pulled and turned the carriages.»

  

Δρ. Απόστολος Ε. Παπαφωτίου

Πολιτικός Μηχανικός Ε.Μ.Π.

Οικονομολόγος Ε.Κ.Π.Α.