Diolkos of Corinth; the largest ship trackway in antiquity

In this post we present selected parts of the paper titled “The largest ship trackway in ancient times: the Diolkos of the Isthmus of Corinth, Greece, and early attempts to build a canal“, by Walter Werner.


Introduction The Peloponnese is connected to the mainland of Greece by the Isthmus of Corinth. Only this narrow land bridge, about 6km wide, prevents the Peloponnese from being an island. The Gerania Mountains are situated to the north, to the south those of Onea. Both are connected by a ridge 85m high which acts like a dam. Channels and narrow land bridges are geographical features of political, economic and cultural importance. Across the Isthmus runs a wall, the Hexamilia, a defence line which was rebuilt on various occasions, such as during the war between the Greeks and Persians. Since ancient times, the north–south trade route made use of this Isthmus. Today a railway line and the road from Athens to Patras runs across it, but for east–west traffic it presents a great obstacle. In the past, ships had to sail around the Peloponnese in order to go from the Saronic Gulf to that of Corinth. This meant doubling dangerous capes, in particular Cape Malea in the south of the Peloponnese. The importance of the Isthmus of Corinth lies in its strategic position. The city of Corinth for many years controlled traffic between the Aegean and Ionian Seas. During the reign of Periander (625–585BC) the city of Corinth reached its prime. Periander kept a large fleet to control shipping on both seas. For transporting the vessels from one shore to the other there was a ship trackway, the Diolkos. This system of transporting ships was mentioned for the first time by Thucydides in the period of the Peloponnesian War (late 5th century BC) and later by Strabo, Pliny the Younger, Polybius, Aristophanes and Dio Cassius.


The Diolkos 

Dating It is not known when the Diolkos was constructed. For Thucydides the Diolkos was something already ancient. The carved characters and monograms which can be seen on the surviving stonework appear to date from the period of Periander. Nonetheless, there may have been an earlier but less well-built slipway.


Description Right behind the pilot station at the western entrance of the Corinth canal there is a large area of rectangular stone slabs, sector A; its surface slopes towards the canal. It is not known whether this slope already existed in antiquity or whether it is the result of building operations for the canal. It is made up of slabs of various sizes and extends about 10m N–S by 8m E–W. Carved stones lying in the present canal indicate that this area was once larger in both directions. Loosely laid stones are visible for a length of 27·5m. There are slabs even beyond this point and originally this area must have been 50m long. There are no cart tracks or other wear marks. The end of the ancient Diolkos shows clear signs of the destructive power of present-day shipping; as a result of wash, some of the flagstones have become loose and there is the danger of their slipping into the canal.

To the south of this paved area, sector B, the real end of the Diolkos lies separated by a low mound of spoil. Its breadth varies between 5·8 and 5·9m while the length of the interior comes to 24·55m. This U-shaped building is not in a direct line with the trackway, which starts further to the east. The Diolkos should lie buried under 1m of sand further to the west. Sector A must have been used for keeping the vehicles ready and therefore no wheel tracks can be found there.


During the excavation of sector C at the southern side of the canal, characters and monograms were unearthed in great numbers. On some stones there are one or more incised signs. The suggestion that these symbols were a kind of signal is difficult to accept today. Instead they must have been marks for adjusting the vehicles.

The most interesting parts of the track-way lie inside an area used by a Greek military engineering unit. The first part of the Diolkos in this area has disappeared completely. It then runs on with a slight bend to the right with a radius of 500m. At this stage, the tracks, which were deliberately cut into the slabs, are clearly visible. Their role was to guide the cart wheels. It is surprising that here the tracks are very well preserved, while at other stages none or only shallow ones are visible. The gauge remains a constant 1·5m. Since the Diolkos was in use for many years one would have expected deep abrasion marks along the whole length.


An unusual feature is the side tracks accompanying the two parallel maintracks. It is uncommon for these to be cut so deeply into the rock. They are separated from the main track and join them again later. These side tracks can be explained if we compare them with the run of along vehicle, because the fixed axle at the rear takes a shorter route, as in a bend. This also explains the different depth of the tracks.

Further to the east, there are two parallel rows of stones on the trackway. It was their unearthing by a bulldozer which led to the discovery of the Diolkos inside the military area. Both the stone ramps are next to the northern track. The southern guiding row consists of  22 carved stones which add up to a length of about 15m, while the northern one is a little shorter. These stones measure 0·4m in height. They are no longer in their original position as they have been moved diagonally and have also been canted up. Most probably their task was to guide the wheels of the vehicles. Within this guide-stone stage no, or hardly any, cart tracks were visible.


On the southern guiding row, narrow grooves have been ground into the upper side. They should not be regarded as wheel tracks, but as the chafe marks of ropes. Most probably these marks are contemporary with the wheel tracks along the Diolkos, as it is rather unlikely that they relate to an earlier period.

The last stage towards the east has been removed in modern times and terminates in a military car park. The Diolkos runs beneath it and cannot be excavated. Beyond this spot and outside the military area the ship trackway has been traced during archaeological work.


Reconstruction The builders of the Diolkos did not choose a straight line, but one which fitted with the landscape. They preferred a curved course in order to avoid, not only the removal of larger quantities of earth, but also steeper gradients.

The Diolkos climbs across the lowest pass of the Isthmus. Had it been a direct line the total length would have measured only 5857m, but then the trackway would have had to ascend a height of over 79·19m. The gradient would have been as much as 1:37 while the selected routes reaches only 1:70. This rise is not a constant one, as it is greater in the central section than towards either coast. That part of the Diolkos which leads towards the Bay of Corinth is still visible and other parts have been excavated. It has always been assumed that the ship trackway runs in a straight line to the east.

The total length of the Diolkos adds up to 8000m due to its southern run. Since there are already two bends in the excavated part, further bends can be expected along the other parts of the Diolkos which pass over higher ground.


Construction and use Ancient writers tell us little about how ships were transported across. In the sources only ‘dragging across’ or ‘transporting’ are mentioned. In one of his plays Aristophanes gives an offensive–erotic comparison with the Isthmus of Corinth in the line ‘… from here to there faster than someone from Corinth’ (Thesm. 648).

The transportation of heavy goods was nothing unusual in ancient Greece. The erection of temples, theatres and arenas are clear signs of this ability. The forty columns of the temple of Apollo in Corinth (550–525BC) were monoliths. Each column weighs 26 tonnes, has a height of 7·21m and a diameter of more than 1·30m, while the architrave blocks each weigh 10 tonnes. It is known that column drums for the city of Eleusis came from a quarry 35km distant. The transport system for heavy goods was well developed in that period; in an inscription on the Parthenon in Athens (448–532BC) wheel wrights, carters and transporters are mentioned. Diodorus Siculus (1st century BC) tells us about transport vehicles with several axles, which were specially constructed for the building of a temple. Livy refers to the transportation of ships from the Mare Piccolo to the Mare Grande near Tarento. For this purpose ‘… all kinds of vehicles were collected, joined together, and lifting devices were brought near’ (Livy, XXV11,18). This means that more than one vehicle was used for each ship. The relief of a calendar frieze of Hagia Eleutherios shows how this could have been done: two under-carriages with two axles are placed under a processional ship. This helps us to imagine the method of transportation over the Diolkos.


How the ships were transported? With the use of wheeled vehicles. Lifting the ships with the help of derricks onto the under carriages would have been within technical capacities. Warships had, as a kind of inner stay, constructions of rope, the hypozomata. These were thick ropes running between the stem and the stern directly beneath the deck. Their task was to reduce the sagging and hogging of the hull. Most probably similar guys were used above the hull during transport.

For moving the vehicles along the Diolkos some kind of propulsion was needed. A trieres, the Greek oared warship, displaced an estimated 21 tonnes without, and about 27 tonnes with, equipment (Morrison& Coates, 1989: 68; 1990: 231).


On a permanent installation such as the Diolkos, technical devices can be expected to have ensured that the transport was safe and fast. ‘Spanish windlasses’ and pulleys were certainly available. The words of Thucydides in the summer of 428BC ‘…and erected machinery on the Isthmus…’ (Thuc., III, 15) can only mean that technical gear and ropes were overhauled. The speed of the transport much have been comparatively high, in the words of Cleisthenes above, since the people of Corinth could look back on a long experience. Propulsion must be imagined with men and animals pulling on ropes with the help of tackles and blocks. Warships, which were always oared vessels, had their own propulsive power with them, in the case of a trireme, 170 oarsmen on each ship; these had to move about 21 tonnes, or say, 125kg per man. In 220BC, Demetrios of Pharos had a fleet of about 50 vessels dragged across the Isthmus to the Bay of Corinth by his men. For this they received extra pay (Polyb., IV, 19).

Thucydides, the great ancient historiographer, mentions that during the Peloponnesian War (431–404BC) the Diolkos was used for transporting warships across the Isthmus. He refers to this transportation of ships as something fairly obvious, as if this was a long-standing tradition.

After the battle of Actium in 31BC, Octavian used the Diolkos to take his fleet as fast as possible towards Asia: of his 400 vessels, 260 were constructed in the ‘liburnian way’, smaller, lighter galleys, and it was part of this fleet which crossed by the Diolkos to the Saronic Gulf. In AD 868, the Byzantine admiral Niketas Oryphas had his whole fleet of 100 dromons dragged across the Isthmus; according to the report the crossing was executed quickly and with great skill.


Canal The idea of digging a canal through the Isthmus of Corinth is an old one. The Diolkos, the ship trackway, could not meet all the needs of either naval or merchant ships. A number of attempts were made in antiquity. Periander of Corinth (c. 625–585BC) planned a canal, but did not continue work on it because he was afraid that Corinth might lose its economic power. In the same way that modern Corinth did not gain any economic advantage from the present canal (unlike the City of Patras), ancient Corinth might have lost its ruling position as an entrepôt for goods.

Julius Caesar (100–44BC) considered digging a canal, along with other projects reported by Suetonius. The plan certainly had strategic–military reasons, but it also would have made a shorter safe passage for merchant ships hailing from the East. The assassination of Caesar in 44BC put an end to all these plans.

While taking part at the Isthmian Festival, Nero remembered the failures of his predecessors to build the canal. The ambitious ruler sent a group of surveyors to the Isthmus. The work was started by a ceremonial opening. Nero made a speech, made the obligatory first cut with the spade and carried away the first basketful of earth. The labour force consisted of 6000 prisoners from Judaea which Vespasian had sent. The operation probably began in AD 67. Rebellions ending with the suicide of Nero prevented the completion of the canal.


Conclusion It was many centuries before the Corinth canal became a reality. Between 1881 and 1893 work was undertaken by various companies. Many technical and financial difficulties had to be overcome before the canal opened in 1893. The centenary in 1993 was a quiet event. Knowledge of the Diolkos seems to be lost. In travel guides it is hardly ever mentioned and then only with a few lines. The largest ship trackway in antiquity deserves better public attention.


Research-Selection for NovoScriptorium: Philaretus Homerides





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