Will it Last 5,000 Years?

That is the premise of this article in Scientific American from 1927. The Thirteenth Century French style nave is marked by great simplicity and dignity. It has the fundamental characteristics of the cathedrals of Notre Dame, Chartres, Ameins and Rheims. Among these, the interior of St. John’s nave is unmatched for sheer majesty. A review of the building methodology of the nave goes a long way to answer the question. Will it last 5,000 years?

Both the exterior granite and the interior limestone in themselves will last that long. So, what other factors can determine how long that building will last? The author, an engineer, suggests three: design, poor ancillary materials and workmanship. He suggests that St. John’s greatly surpasses, in its structural strength and workmanship, the cathedrals of the Middle Ages.

The Design Compromised by Material Availability

The drawing above compares a pier in Gloucester Cathedral (1100 A.D.) and one of the intermediate piers of St. John’s. The builders of the Twelfth Century Norman Church, and all the later medieval churches, could not afford to construct their piers of cut stone throughout. They built an exterior shell of fine squared stone, from six to twelve inches thick. They then filled the center with a core of rubble set in lime mortar.

When the load of the upper walls came upon such piers, the rubble core settled more readily than the carefully jointed ashlar casing. With the passage of centuries, the mortar frequently disintegrated and the center rubble core lost its bearing quality. The whole load rested on the thin outer shell, which would bend or bulge, flakes of stone splitting off, and the work threatening an early fall.

The more slender intermediate piers of St. John’s have amazingly slender proportions, a diameter of 5 feet to a length of 98 feet. To guard against any buckling under the load they carry, each course became a single granite block. These blocks weigh up to 4 tons each, set with thin cement mortar joints.

Medieval Churches Limited to Small Stone

In those early days, money was scarce and the world had lost many of the secrets of construction, notably that of the making of the cement. This was the ingredient that made for the lasting work of the Romans. It was an age of small stone and mortar construction. Lack of suitable tools and appliances at the quarries, poor roads and inadequate means of transportation had an impact. This and the lack of capital drove the early builders to the use of small size building stone. In binding this material together, they were restricted to the use of lime mortar. Some of this was good, but much of it, as many a catastrophe proved, of wretched quality.

The Main Piers

The main piers measure 11 feet by 16 feet, 3 inches. They consist of a heavy outer casing of multiple ton Indiana limestone with an inner core of massive squared granite blocks. Each granite block weighs between 5.5 and 7 tons.

Towers Collapse and Piers Buckle in Medieval Cathedrals

In both English and French cathedrals built in the Middle Ages there have been many building problems. Chichester, Ely, Wells, Salisbury and Beauvais have experienced these problems as well as tower collapses, failures and the need for heroic measures to shore up the building. The settlement of the masonry under the thrust and counter thrust of vault and flying buttresses have caused much of this.

St. John’s has been designed and built with a careful avoidance of the pitfalls which so often brought disaster to certain medieval churches. The load upon every pier, the thrust against every buttress, has been calculated with close exactness. The crushing strength and the safe limit of loading of each kind of stone are known.

This cross-section illustrates the strength and mass of the abutments. The thrust of the nave vault, great though it may be, will never push these huge masses of out of plumb. They may well be in place for 5,000 years.

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• Building for the Ages, J. Bernard Walker, Scientific American, November 1927
• All images and drawing are from the above article as is the 5,000 Years question.