Pergamon Bridge
Encyclopedia
The Pergamon Bridge is a Roman substruction bridge
over the Selinus river (modern Bergama Çayı) in the ancient
city of Pergamon
(today Bergama
), modern-day Turkey
. The 196 m (643 ft) wide structure, the largest of its kind in antiquity
, was designed during Hadrian
's reign (AD 117–138) in order to form a passageway underneath a large court in front of the monumental "Red Basilica
" temple complex. The two intact tubes, which consist of supporting walls covered with barrel vault
s, still serve their purpose to this day.
For urban development, such substructions are regarded as particularly useful for providing large open spaces in densely-populated inner city areas. This was also the case in Pergamon, as the building of the Serapis Temple required the bridging of an entire section of the River Selinus in order to create sufficient space for a large platform in front of the temple.
A similar urban project was also executed in another ancient Anatolian
city, Nysa
, where the 100 m (328 ft) wide Nysa Bridge
supported a theatre
forecourt.
The dimensions of both semi-circular arches
are practically identical: the clear spans are 9 m (30 ft) each, the rise from the springing line to the apex of the arch 4.5 m (15 ft) and the clearance to ground level measures 7.5 m (25 ft). The vaults are built of rubble bound with mortar, and rest on an ashlar stone base.
Up- and downstream of the bridge substruction are another two well-preserved ancient bridges across the Selinus, called Tabak Köprüsü and Üc Kemer Köprüsü ("Three Arch Bridge").
s has been the subject of hydraulic
and hydrological
research. The gradient of the tunnel was calculated as 0.6 % with a maximum discharge capacity of 360 m³/s. Exceeding this limit puts the bridge under internal pressure and damages the structure in the process. Considering that the Selinus is 13.4 km (8.3 mi) long, with a median
gradient of 2.2 % and a drainage basin
of 101 km² (39 sq mi), the following median intervals were calculated, depending on the method employed:
250 years (Günerman method)550 years (D.S.I. method)
The study came to the conclusion that statistically every 700 years, a value which has been referred to as the "arithmetic mean
", floods are to be expected which would exceed the capacity of the bridge.
Roman bridge
Roman bridges, built by ancient Romans, were the first large and lasting bridges built. Roman bridges were built with stone and had the arch as its basic structure....
over the Selinus river (modern Bergama Çayı) in the ancient
Ancient history
Ancient history is the study of the written past from the beginning of recorded human history to the Early Middle Ages. The span of recorded history is roughly 5,000 years, with Cuneiform script, the oldest discovered form of coherent writing, from the protoliterate period around the 30th century BC...
city of Pergamon
Pergamon
Pergamon , or Pergamum, was an ancient Greek city in modern-day Turkey, in Mysia, today located from the Aegean Sea on a promontory on the north side of the river Caicus , that became the capital of the Kingdom of Pergamon during the Hellenistic period, under the Attalid dynasty, 281–133 BC...
(today Bergama
Bergama
Bergama is a populous district, as well as the center city of the same district, in İzmir Province in western Turkey. By excluding İzmir's metropolitan area, it is one of the prominent districts of the province in terms of population and is largely urbanized at the rate of 53,6 per cent...
), modern-day Turkey
Turkey
Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...
. The 196 m (643 ft) wide structure, the largest of its kind in antiquity
Ancient history
Ancient history is the study of the written past from the beginning of recorded human history to the Early Middle Ages. The span of recorded history is roughly 5,000 years, with Cuneiform script, the oldest discovered form of coherent writing, from the protoliterate period around the 30th century BC...
, was designed during Hadrian
Hadrian
Hadrian , was Roman Emperor from 117 to 138. He is best known for building Hadrian's Wall, which marked the northern limit of Roman Britain. In Rome, he re-built the Pantheon and constructed the Temple of Venus and Roma. In addition to being emperor, Hadrian was a humanist and was philhellene in...
's reign (AD 117–138) in order to form a passageway underneath a large court in front of the monumental "Red Basilica
Red Basilica
The "Red Basilica" , also called variously the Red Hall and Red Courtyard, is a monumental ruined temple in the ancient city of Pergamon, now Bergama, in western Turkey. The temple was built by the Roman Empire, probably in the time of Hadrian and possibly on his orders...
" temple complex. The two intact tubes, which consist of supporting walls covered with barrel vault
Barrel vault
A barrel vault, also known as a tunnel vault or a wagon vault, is an architectural element formed by the extrusion of a single curve along a given distance. The curves are typically circular in shape, lending a semi-cylindrical appearance to the total design...
s, still serve their purpose to this day.
Classification as bridge substruction
Although the Pergamon Bridge is, due to its extraordinary width, often misleadingly called a tunnel, it should rather be treated as a bridge substruction, since the entire structure was erected above ground, which necessitates construction techniques more akin to bridge building and very different from those employed in subterranean tunnel-driving.For urban development, such substructions are regarded as particularly useful for providing large open spaces in densely-populated inner city areas. This was also the case in Pergamon, as the building of the Serapis Temple required the bridging of an entire section of the River Selinus in order to create sufficient space for a large platform in front of the temple.
A similar urban project was also executed in another ancient Anatolian
Asia Minor
Asia Minor is a geographical location at the westernmost protrusion of Asia, also called Anatolia, and corresponds to the western two thirds of the Asian part of Turkey...
city, Nysa
Nysa, Anatolia
Nysa was an ancient city of Caria in Anatolia, whose remnants are now in the Sultanhisar district of Aydın Province of Turkey, east of the Ionian city of Ephesus....
, where the 100 m (328 ft) wide Nysa Bridge
Nysa Bridge
The Nysa Bridge is a late imperial Roman bridge over the Cakircak stream in Nysa , in the ancient region of Caria, Turkey. The long substructure was the second largest of its kind in antiquity, after the Pergamon Bridge.- Dating :...
supported a theatre
Roman theatre (structure)
The characteristics of Roman to those of the earlier Greek theatres due in large part to its influence on the Roman triumvir Gnaeus Pompeius Magnus. Much of the architectural influence on the Romans came from the Greeks, and theatre structural design was no different from other buildings...
forecourt.
Vault structure
The bridge substruction features two parallel and linear barrel vaults which are separated by a continuously running partition wall. While the uphill entrances of the double tube are on the same level, the exits on the down-valley side are spaced at a 13 m (43 ft) interval, leading to a significant difference in length between the western (183 m (600 ft)) and the eastern branch (196 m (643 ft)). Due to a later built-in 2 m (7 ft) high threshold, parts of the western tube are today silted up.The dimensions of both semi-circular arches
Arch
An arch is a structure that spans a space and supports a load. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures.-Technical aspects:The...
are practically identical: the clear spans are 9 m (30 ft) each, the rise from the springing line to the apex of the arch 4.5 m (15 ft) and the clearance to ground level measures 7.5 m (25 ft). The vaults are built of rubble bound with mortar, and rest on an ashlar stone base.
Up- and downstream of the bridge substruction are another two well-preserved ancient bridges across the Selinus, called Tabak Köprüsü and Üc Kemer Köprüsü ("Three Arch Bridge").
Discharge capacity
The capacity limit of the Pergamon Bridge in case of floodFlood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
s has been the subject of hydraulic
Hydraulics
Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...
and hydrological
Hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...
research. The gradient of the tunnel was calculated as 0.6 % with a maximum discharge capacity of 360 m³/s. Exceeding this limit puts the bridge under internal pressure and damages the structure in the process. Considering that the Selinus is 13.4 km (8.3 mi) long, with a median
Median
In probability theory and statistics, a median is described as the numerical value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to...
gradient of 2.2 % and a drainage basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
of 101 km² (39 sq mi), the following median intervals were calculated, depending on the method employed:
250 years (Günerman method)550 years (D.S.I. method)
- 1,100 years (Mockus method)
- 8,500 years (Snyder method)
The study came to the conclusion that statistically every 700 years, a value which has been referred to as the "arithmetic mean
Arithmetic mean
In mathematics and statistics, the arithmetic mean, often referred to as simply the mean or average when the context is clear, is a method to derive the central tendency of a sample space...
", floods are to be expected which would exceed the capacity of the bridge.