The Arch in Architecture

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Arches in Religious Buildings


As the Roman Empire slowly disintegrated and faded away, some of its ideas remained in use, and some did not. The peculiar system of numbers, using the symbols I V X C D and M, sometimes in a very strange ordering, is now mainly used in clocks, and when writing dates in special circumstances.

But the Roman influence on language is still very strong in Europe and other areas where European based languages are spoken, and will probably continue to persist for hundreds, perhaps thousands of years, even though it was, and is, intangible. Such is the power of ideas, and the need for continuity of communication. Attempts to disrupt this continuity have seldom succeeded. An example was the introduction of new names for the months during the French revolution. France, like many other countries, still uses names with Norse and Roman origins in the distant past.

Roman buildings were more obviously durable than words, though in fact more subject to decay: many remain to this day. Even now you can travel on roads that follow Roman alignments, apart from occasional bypasses. You can see great Roman buildings and mighty bridges, along with artistic creations such as statues and mosaics. Wherever the Romans went, they took their building methods with them.

Long after the collapse of Rome as a power, its ideas persisted. When the Normans came to England, in 1066, they set about creating an island-wide organization. In the Domesday book they created a record of all the land and its uses. The architecture they brought is sometimes called Romanesque. If you go into Gloucester cathedral, started in 1089, or the one at Durham, started in 1093, you will see the semicircular arches on massive piers that the Romans used so effectively. Though not as famous as the cathedrals, many little churches in Gloucestershire tell the same story - the Romans had a hand in them, albeit indirectly.

Only later did the builders of Europe master the narrow columns and pointed arches of the Gothic styles. In cathedrals such as those of Durham and Gloucester, and many others, you can see these later styles alongside, or even on top of, the Norman work. In buildings of this size, you can more or less get away with such incongruous mixtures, or perhaps we are merely used to them.   Certainly in a small house it would look very odd to have a bit of Tudor and a bit of Bauhaus and a bit of 1960s suburban.

The pointed arch is actually very strange, because it does not always correspond to the engineering requirements. We can understand this by considering a simple clothes line, and adding a garment at the middle. The line will form a slope discontinuity at that place, with a new, less curved, catenary on either side.

If we now invert the idea, and make an arch with a point load at the top, it will tend to sag, and in fact we ought to make the arch which is pointed by just the right amount. But pointed arches usually have smaller loads over the middle than elsewhere, not larger ones.

The original design for the shells of Sydney Opera House also included pointed vertices, and likewise these corresponded to nothing in the loading. The shells need considerable rigidity to make them stand. Around a church window, the masonry does the job of holding the arch in place, even though the funicular, or line of thrust, is not followed.

The first two pictures below are of the church at Guiting Power in Gloucestershire.  On the left is a lovely Norman or Romanesque entrance. In the middle is a window in a later style, and on the right is a picture downloaded, with kind permission, from Welcome to Isfahan, where you can find a great deal of information and many pictures about Islamic and Iranian architecture and culture.

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In Gloucestershire, in the "wool" churches, you can see a later style that is much lighter and more open than the Romanesque, built in the lovely pale yellow limestone of the region.  Some of these are found in Cirencester, Fairford, Lechlade and Northleach.

The medieval builders became quite daring, and by the use of flying buttresses they could make very tall buildings with huge openings in the walls, in which they placed the coloured windows that passed on the message. In an age when there was no cinema, no television, no advertising boards, and so on, these windows must have created an effect which we cannot imagine, engulfed as we are in a world of information in colour.

Some builders became so daring that parts of the buildings fell down. The roof of Beauvais cathedral, begun in 1225, collapsed in 1284. It took about forty years to repair the damage. By 1569 the cathedral was much bigger, with a spire that soared almost 500 feet/152 m into the air.  Not for long.  In 1573 there was another collapse. Beauvais cathedral was never completed. This is one potential cost of innovation.  Even in the 20th century, accidents like those to the Comet 1s, and some box-girder bridges, showed that extrapolation of known procedures can be a dangerous operation, if not informed by complete theoretical understanding.

If you go into Salisbury cathedral, and if you stand very close to each of the four stone columns that support the tower and the spire, you will see the deflections caused by the enormous loads that the original builders never intended. Salisbury without the spire is now unthinkable, but that is how it was originally designed. From miles around, on a clear day, you know that you are approaching Salisbury. The same thing happens with many another town and city which has a great cathedral, especially if it is on a hill, as at Lincoln.

In Salisbury cathedral too, you can see the beautiful chapter house, with a single narrow column at the centre, supporting an octagonal array of arched vaults.


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The keystone has no structural significance, but it has developed into a decorative element in many buildings. Sometimes there is an unworthy suspicion that the whole arch over the porch or window of a small house, including the "keystone", was cast as one piece of concrete. Note the difference in the second pair of pictures, taken within minutes of each other, caused by the lighting and viewing direction. In the fifth picture the keystones are clearly decorative.

Click here for more about keystones.

PillarsQ.jpg (73101 bytes)This building includes both trabeate and arched designs. The frontage deviates very slightly from straight. What could be the reason for this?  The yellowish "pillars" carry no load at all: they are merely affixed to the front of the building. A frontal view reveals that they are quite strongly bulged, as if to suggest the great load they are supposedly carrying. As the real load-bearing pillars behind (which may themselves conceal steel piers) are perfectly straight, the result is incongruous. Perhaps they are intended as a joke.

Here are some buildings which have various proportions of rectangular and arched windows.

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In Bath, Bristol, Buxton and Cheltenham, for example, you can find arches lying on their sides, like arch dams, in the form of curved terraces of buildings. But these are only geometrical: there is no thrust. Here is an example. The right hand picture shows the cantilevered balconies. Some such crescents actually make a complete circle. Why were the built? Perhaps just for variety. But as they were built for the rich and fashionable, for whom seeing and being seen can be very important, the crescent is ideal, affording as it does a good view of the whole of the included space from any of the dwellings.

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Things do not always turn out as planned, in building as in life. Here are some pictures of St Mary's church, Cowley, near the head of the Churn valley. The pictures below show that the walls of both the North and South sides of the church have been pushed outwards, notwithstanding their great thickness. Buttresses have been added to prevent further movement.

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You can read about the reasons for the leaning walls and buttresses in the pages about arches and religious buildings.