BUILDING WITH MASONRY.
Throughout the Middle Ages, the most prestigious and durable edifices—castles, churches, and palaces—were built of stone. However, the loss of the Roman formula for concrete (a mixture of water, lime, and pozzolanic sand akin to modern Portland cement, to which a coarse aggregate of rubble and broken pottery was added) and its replacement in the Middle Ages by a weak lime mortar made complex masonry ceilings difficult to build. Thus, one of the major achievements of medieval architecture was the recovery of the ability to vault monumental interior spaces to dramatic effect. Medieval masons continued many Roman architectural practices, constructing their buildings with rubble (broken, rather than cut stone) walls faced with cut stone blocks or decorative patterns, as seen in the surviving sections of the late-tenth-century cathedral of Beauvais, Notre-Dame-de-la-Basse-Oeuvre. Yet, there were significant variations from region to region in Europe due to available building materials and established traditions. For example, brick was used in southern France and northern Germany as a substitute for the poor-quality local stone. Ancient Roman architectural elements (remnants of columns, carvings, etc.), called spolia, were often incorporated into medieval Italian structures because of their handy abundance as well as their evocative connection to the glory of the past, while timber forms inspired designs in Anglo-Saxon stone buildings in England.
THE LEGACY OF ROME: ARCHES AND VAULTS.
By far the most important legacy from Rome was the arch, which constituted the basis of medieval church architecture. An arch is a curved structural form composed of wedge-shaped stones called voussoirs. The uppermost voussoir is the keystone which, when dropped into place, locks the other stones of the entire arch together. Pushing against one another, the stones stay in place, and as long as there is enough material around the arch to resist this outward, pushing force, the arch will remain stable. There were many uses for arches: supported by columns or piers to form an arcade, they span space to create passages; they frame doorways and windows; they act as structural reinforcement; and, in miniature, they decorate walls. Arches were, in turn, the basis of vaults. The continuous barrel vault was constructed by extending an arch across an expanse from pier to pier, creating a ceiling that had a concave or half-cylindrical appearance, as occurs in the main nave space at Saint-Sernin at Toulouse, France. Two barrel vaults intersecting at right angles, the "groins" marking the lines of intersection, formed a groined vault. By focusing supporting forces at the corners of the vault compartment or bay, the groined vault relieved the wall of its structural purpose and made large openings and windows possible. But because the stones of the groins had extremely complex geometric shapes, these vaults were difficult to
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build and were used most frequently over smaller spaces that included windows, such as those in the side aisles of Saint-Sernin.
THE COMING OF GOTHIC ARCHES.
European architecture in the eleventh and early twelfth century, despite its variety, is commonly called "Romanesque" because its massive walls, its rounded arches, the extension of stone vaulting throughout the entire structure, and many of its ornamental forms resemble Roman buildings. Around 1100, new forms appeared that moved away from the heritage of ancient building and began to transform the appearance of architecture. The first major development can be seen in a change in the shape of arches. Builders from the Carolingian to the Romanesque periods employed semicircular arches. To draw one with a compass requires only a single fixed center point to produce an arch whose height is always one-half of its span. However, a different type of arch appeared in Romanesque buildings, such as Durham Cathedral, that became the dominant form in the Gothic period from the twelfth through the fifteenth centuries: the pointed arch. In this case, the intersecting arcs are struck from two centers whose location is fluid. This creates an arch that not only can be flexibly tailored to fit almost any spatial need but also is more structurally efficient than the semicircular arch. A second breakthrough came with the invention of the ribbed groin vault. This vault had all the advantages of the groin vault, but added ribs—decorative moldings that masked the groin lines. Ribs facilitated construction, first, because they were assembled from identical pieces and, second, because once built, they offered a scaffolding that was filled in by a light stone membrane or web. An example of vaulting appears in the Chapel of the Heiligen-Geist-Hospital in Lübeck, Germany.
THE FLYING BUTTRESS.
Along with pointed arches and ribbed groin vaults, the flying buttress was introduced as a key structural component in mid-twelfth century buildings such as the Abbey of Saint-Germaindes-Prés and the Cathedral of Notre-Dame, both in Paris, and the Cathedral at Chartres, France. Exposed arches "flying" over the aisles of the church act to brace the wall against the outward thrust of the vault and the wind pressure on the roof and to direct these forces to massive slabs of masonry (buttresses). Flying buttresses, coordinated with ribbed groin vaults and pointed arches,
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composed a completely new system. Rather than a continuous envelope of heavy supporting walls, as was characteristic of the Romanesque style, the structure now resembled the cage of an Erector set, with the flying buttresses appearing both internally and externally. By exploiting the potential of these new features, Gothic church architecture was able to achieve the impossible: unprecedented height combined with walls that were little more than perforated screens whose openings were filled with vast fields of dazzling stained glass.
Most buildings in the Middle Ages—houses, forts, barns, market halls, and even parish churches—were made of timber. Stone construction itself required vast quantities of wood for the temporary scaffolds socketed into walls that served as work platforms in upper levels, for formwork upon which vault stones were laid, and for templates or patterns that guided the cutting of moldings. Cranes and the great wheels that hoisted building materials aloft were made of wood. Timber pilings and lattices were incorporated into the foundations of edifices that rose on marshy ground, a technique still used in the late nineteenth century in Henry Hobson Richardson's Trinity Church in Boston. Wooden vaults, imitating the appearance of stone, were erected at York Cathedral in the late thirteenth century, and the fourteenth-century crossing of Ely Cathedral, its stone lantern perched atop a pinwheel of wooden vaults, achieved one of the most spectacular spaces of the age. But, by far, the most significant concern of carpentry was the roof structure.
Tall, steeply pitched roofs were more than practical coverings to shed the rain and snow of northern Europe's inclement weather; they were status symbols. Hrothgar's magnificent "mead-hall" of Heorot is described in the early (pre-tenth century) Anglo-Saxon poem Beowulf as "high-roofed—and gleaming with gold," and the slate roofs of the palace of the kings of France in Paris struck one fourteenth-century writer as "glistening bright" to the point that "everyone is gladdened by / The very thought of entering." Churches, too, were crowned by prominent roofs whose beams were likened by a late thirteenth-century bishop, William of Mende, to "the princes and preachers who defend and fortify the unity of the Church," while the tiles reminded him of "the soldiers and knights who protect the Church against the attacks of enemies of the faith." Until the
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eleventh century, large interior spaces in medieval churches were covered by timber roofs, often open to the space below, devised from a system of members, that included sloping beams called rafters whose ends were connected by horizontal tie beams, to form a triangular truss. Norwegian stave churches, a late example of which is found at Borgund (c. 1250), demonstrate the advanced roofing technology achieved in northern Europe. Trusses, stiffened by curving scissor braces, are supported by tall timber posts or staves to create a bay system that may have influenced the development of a comparably integrated frame in stone architecture.
STONE VAULTS, TIMBER ROOFS.
With the spread of masonry vaulting in the Romanesque period, carpenters faced a set of problems that tested their ingenuity. The curving crown of the vault that rose into the space of the roof made it impossible to create a structure based on trusses placed every three or four feet as in an un-vaulted building, and they were forced to search for solutions that accommodated the vault but did not sacrifice stability against gravity and wind. The number of tie beams was reduced gradually as supplementary rafters and braces were added to increase the rigidity of the roof frame. In Gothic architecture of the thirteenth and fourteenth centuries, roofing systems evolved in response to the wide spans of the spaces and the reduction of the thickness of the walls. At Notre-Dame in Paris and Reims Cathedral, trusses were organized into bays consisting of main frames, recognizable by their vertical hangars that support a matrix of beams and rafters that alternate with secondary frames without tie beams. More important, plates that ran along the top of the wall and purlins that supported the additional rafters integrated the system longitudinally. Reaching a pitch of about 60 degrees, these steep roofs emphasized the vertical silhouette of the soaring buildings, making them appear even taller.
Timber architecture was not simply a question of money, nor was it indicative of social class. At Aachen, where Charlemagne's audience hall and chapel were built of stone, the emperor maintained his domestic quarters in a wooden structure. As medieval literature, from Beowulf to Sir Gawain and the Green Knight (1360–1370) makes clear, the hall stood at the center of palace life, serving as the stage for aristocratic
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festivities. But it was also the basis of other structures of daily life such as hospitals, colleges, and commercial buildings. In stark contrast to the arched form of churches, halls were fashioned of vertical post and horizontal beam construction that created aisled interior spaces. After around 1200, there was a general shift toward aisleless structures that is represented by the remarkable rebuilding of Westminster Hall in the palace of the kings of England. Completed in 1099 by the Norman ruler William Rufus, who is reported to have "spared no expense to manifest the greatness of his liberality," the original hall was so wide—around 67 feet—that internal supports were required to carry the ceiling. In the 1390s, Richard II engaged his chief carpenter, Hugh Herland, and master mason, Henry Yevele, to refurbish the hall. Herland's ingenious hammer-beam roof, supported through the use of short cantilevered timbers, covered the enormous space with a single breathtaking span. The hammer beams, projecting from the wall, actually pull in the sloping rafters to keep them from spreading outward. Combined with the heavy vertical
hammer posts and horizontal collar beam (tie beam) as well as the great arch, they transmit the weight and thrust of the roof to the stone brackets, or corbels, located about halfway up the wall, that had been added by Yevele. Masonry and carpentry collaborate in a structure that is at once logical and elegant. Despite the fact that some 600 tons (the weight of a modern diesel locomotive) of oak were used in the frames, the roof—enriched by open grilles—appears to float on the backs of the angels that decorate the ends of the hammer beams. Finally, it is important to remember that this great roof structure was assembled from material provided by trees grown in forests that were legally protected and carefully managed. Eliminating the floor posts was not simply a matter of artistic choice, but permitted the use of smaller trees that were easier to cut and transport. The study of medieval structures reveals the complex interrelationship between architectural form, building technology, natural resources, and human institutions.
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François Bucher, "Medieval Architectural Design Methods 800–1560," Gesta 11 (1972): 37–51.
Ragnar Bugge, Norwegian Stave Churches. Trans. Ragnar Christophersen (Oslo, Norway: Dreyer, 1953).
Nicola Coldstream, "Architecture," in The Cambridge Guide to the Arts in Britain. Vol. 2: The Middle Ages. Ed. Boris Ford (Cambridge, England: Cambridge University Press, 1988): 42–87.
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—, ed., Architectural Technology up to the Scientific Revolution (Cambridge, Mass.: MIT Press, 1993).
Harold M. Taylor and Joan Taylor, Anglo-Saxon Architecture (Cambridge, England: Cambridge University Press, 1965–1978).