POINTED ARCHES

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Ancient primitive arches were triangular arches created by offsetting each layer until the gap was closed.
Etruscan semicircular arches were built by placing blocks shaped like truncated wedges over a temporary wooden form.
Early Christians knew that a long arch made of many nearly rectangular blocks had a tendency for the center blocks to fall in. The early Christians would prevent this by making flatter arches that increased the horizontal forces, or by making the arch slightly pointed at the top.
Zoroastrians and Muslims copied these Christian solutions.
Someone (likely Adelard of Bath) brought the slightly pointed arch to Christian Europe. He also brought an Arabic translation of Euclid’s “Elements” that mentioned the strength of triangles. Soon afterward, Europeans were building very pointed arches.
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Image cropped from image by Jean Housen, via Wikimedia Commons.

image credit

https://commons.wikimedia.org/wiki/File:20090727_mykines33.jpg#mw-jump-to-license

THE EARLIEST POINTED ARCHES

Ancient primitive pointed arches were constructed by leaving a several meter gap at the bottom of a wall being built of flat stones, and gradually narrowing the gap as each added layer of flat stones was offset a bit. When the gap narrowed to only a quarter of a meter or less, a lintel stone was placed over the gap.

EARLY SEMICIRCULAR ARCH
Semicircular arches were built upon a temporary semicircular wooden arch. An early semicircular arch is the Ishtar Gate, reconstruction shown at https://upload.wikimedia.org/wikipedia/commons/thumb/e/e3/Ishtar_Gate_at_Berlin_Museum.jpg/220px-Ishtar_Gate_at_Berlin_Museum.jpg I estimate it spanned a distance of 4 meters (13 feet), which may be close to the limit for a semicircular brick arch, or else the center brick would fall out.

ROMAN ARCHES
Roman arches, copied from Etruscan arches, usually formed 180 degrees of arc (a semicircle), and had an odd number of blocks in the shape of precise truncated wedges.

There are a few examples surviving of less than 180 degrees “flattened” arches built of concrete (instead of bricks or stones) in Rome, such as some of the arches of the 2nd century Villa of the Quintilii, and arches in the tunnels under the Coliseum. This would direct more of the force horizontally, requiring thick walls at each end. Some bridges that could be anchored at both ends by a hillside also used flattened arches.

BYZANTINES
The Christian Byzantines and Zoroastrian Persians used smaller blocks, sometimes in 2 layers. In larger arches there were so many blocks that the truncated wedges were almost rectangular in shape.

To prevent the center stones from falling out, the arch was flatter than most Roman arches, with only about 110 degrees of arc instead of 180 degrees of arc. This increased horizontal forces to keep the center stones in place, but required a thick wall to restrain each end of the arch.

BYZANTINE CHRISTIAN SLIGHTLY POINTED ARCH

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Original Image by Jorge Lascar, via Wikimedia Commons.

cropped and digitally enhanced by William Siepmann
[I (William Siepmann) release my digitally enhanced version of a portion of his image under the same Creative Commons restrictions as the image by Jorge Lascar
image credit
https://en.wikipedia.org/wiki/File:The_Church_of_the_Holy_Sepulchre-Jerusalem.JPG
The Byzantine Church of the Holy Sepulchre in Jerusalem, built in the year 335, has an arch (180 degrees, semicircular, built of several layers of small blocks), has an even number of stones, is slightly pointed at the top, to prevent the plair of center stones from falling out. I digitally processed a photograph of it to enhance the detail.


MUSLIM SLIGHTLY POINTED ARCH
Muslim architects (400 years after the Church of the Holy Sepulchre) in the 8th century built the Fortress of Al-Ukhaidir (also called the Abbasid palace of Ukhaidir) and the Cistern of Ramla, which used slightly pointed arches similar to those that had been used in the Byzantine Church of the Holy Sepulchre.

[It is important that a high quality photograph be examined to determine whether or not an arch is pointed. If a photograph of a round arch is blurred or not well lit, the inner wall of the “tunnel” of the arch cannot be distinguished from the face of the arch, creating the illusion of an asymmetrical very pointed arch.]
Ramla is located between Jerusalem and Tel Aviv.


A high resolution photograph of the arches of the underground water storage facility at Ramla is on the website of http://biblewalks.com/info/info.html
The link to the image is
http://www.biblewalks.com/Photos137/ArchesPool1.jpg
The arch had a full 180 degrees of arc, slightly pointed where the left half of the arch met the right half of the arch.
These had two layers of an even number of crude truncated wedges, with no keystone.

 

VERY POINTED CATHEDRAL ARCHES
Someone around the year 1120 brought the concept of the slightly pointed arch to Christian Europe. Most likely it was the English astronomer and mathematician Adelard of Bath, who visited Muslim lands. Around the year 1120, he brought back to Europe books in Arabic of the observations of Muslim astronomers, and an Arabic translation of Euclid’s “Elements” (written around the year 300 BC in the Greek city of Alexandria Egypt) that mentioned the strength of triangles.

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Bonne-Espérance Abbey, Vellereille-les-Brayeux, Belgium
Image by Jonathan Nélis, via Wikimedia Commons.
Image credit https://commons.wikimedia.org/wiki/File:Bonne-Esperance_Salle_capitulaire.JPG#mw-jump-to-license

13th century, Bonne-Espérance Abbey, Vellereille-les-Brayeux, Belgium

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Original image by Jonathan Nélis, via Wikimedia Commons.
Image was digitally enhanced by Wiliam Siepmann.
[I (William Siepmann) release my digitally altered version of the image under the same Creative Commons restrictions as the Jonathan Nélis photograph I copied from.]
Image credit https://commons.wikimedia.org/wiki/File:Bonne-Esperance_Salle_capitulaire.JPG#mw-jump-to-license

The ceiling was made of brick reinforced with stone ribs and stone arches.
At the top of the image are ribs (made of 3 layers of stone blocks) in the ceiling above the intersection of two barrel vaults. Both the Romans and the Muslims had used ribs in domes and in barrel vaults, but the Christian architects of the cathedrals were the first to use ribs in the ceiling above the intersection of barrel vaults (replacing the Roman groin vault with a ribbed vault).
[A Muslim website I visited showed a photograph of a Muslim groin vault but falsely identified it as a ribbed vault.]
At the bottom of the image are pointed arches constructed of 4 or 5 layers of stone.


VERY POINTED MUSLIM ARCHES
Mosques that do have very pointed arches were not built until after European Christians invented the very pointed arch.
For example, Alhambra in Spain was built in the mid 13th century, the Bibi-Khanym mosque in Uzbekistan was built in 1404, the Miri-Arab Madrasah in Uzbekistan was built in 1536.

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