Vitruvius describes the craft of opus sectile–the laying of pavements composed of pre-cut pieces of colored marble, granite, porphyry and other stones, which are arranged to form decorative patterns and images. The art was practiced continuously into the Middle Ages in Byzantium, but lapsed in the West, with the exception of the Byzantine cultural outposts Ravenna, Venice and Sicily. During the mini-Renaissance of the 12th century the Cosmati, a family of stone cutters, sculptors and masons, originally from Anagni, revived the ancient art in Rome itself.

Over several generations, the Cosmati created a series spectacular pavements, made from the seemingly inexhaustible supply of spolia, masonry leftovers and broken fragments of expensive, exotic stone for many venerable Roman monuments, including Santa Maria Maggiore, San Giovanni in Laterano, Santa Croce in Gerusaleme, San Crisogono, and newly-rebuilt churches such as the Aracoeli, San Clemente, Santa Maria in Cosmedin and Santa Maria in Trastevere.

Following ancient models, the pavements balance broad colored bands and medallions (slices of toppled columns) with intricate borders and interstitial areas composed of minuscule shards. The underlying ordering principle of interlaced geometry is manipulated to create optical conundrums. The basic pavements are composed of white Greek and Italian marble, serpentine and porphyry. The extent of the Roman Empire gave its wealthy citizens access to rare varieties of marble and granite quarried in north Africa, Asia Minor, pieces of which were incorporated into more elaborate Cosmati floors.

The more opulent Cosmati pavements are a hybrid opus sectile/mosaic technique, derived from southern Italian and Sicilian sources, that incorporates glass tesserae with gold backgrounds into the patterned stone. The contrast of glittering, reflective gold and opaque deeply colored stone gives Cosmati work its distinctive brilliance.

While the original patterns and coloration have been preserved, much of the actual stone in the Roman Cosmati pavements has been relaid many times as floors settled and marbles cracked. The pristine pavement in the Lateran basilica, for example, contains no medieval stone; the only Cosmati pavement in Rome that has never been relaid is in San Benedetto in Piscinula. The pavements of the provincial churches of Terracina, Ferentino, Tarquinia, and Anagni are less-heavily restored.

The Cosmati operated a large workshop. Their students, studio assistants, and later, their imitators, disseminated the house style far beyond Rome: “cosmatesque” pavements are found across the entire Italian peninsula in churches either built or rebuilt in the 12th and 13th centuries. In the 1260s, Henry III, a great connoisseur of art, commissioned a “cosmatesque” pavement and shrine for the tomb of Saint Edward the Confessor, located in the sanctuary of Westminster Abbey. The the fact that Henry chose a Cosmatesque pavement for the most important part of a church recently rebuilt in the most up-to-date French Gothic style suggests something of the prestige, luxury and novelty of Italian opus sectile.