Zellij

Zellij begins as plain squares of glazed terracotta, fired whole in the kilns of Fez in white, honey yellow, green, turquoise, blue and near-black. The geometry enters through the hand. A cutter takes a fired square and, with a sharp-edged hammer, strikes out from it one small shape at a time: stars, almonds, darts, straplets, each piece a standard form of the craft's repertory, sized to fit its neighbours exactly. The precision demanded is severe, since a panel may hold thousands of tesserae and an error of a millimetre repeated across a lattice would shear the whole design. The assembly is stranger still: the pieces are laid out face down on the ground, glaze against the earth, following the pattern in mirror image and from memory.

Wet mortar is poured over the backs and left to set, and only when the hardened slab is lifted and turned does the maker see the face of what was made. The knowledge lives in apprenticeship. A boy enters a workshop young, spends years learning to cut each canonical shape before he is trusted with composition, and rises, if he rises, to maalem, master. The craft has been transmitted this way in Fez without interruption since the Marinid madrasas of the fourteenth century received their great revetments, which makes zellij not a revival but a survival: one of the few places on earth where a medieval geometric art is still practised with the medieval division of labour intact.

Nearly every classic zellij panel radiates from a khatam, the eight-pointed star made by laying one square over another at forty-five degrees. The khatam is the seed of the composition. Around it the cutter sets rings of strapwork, interlacing bands that widen outward ring by ring, and the geometry is so ordered that the radiation could in principle continue without limit; the panel ends where the wall ends, not where the pattern does.

From the same grammar the masters of Fez developed rosettes of far higher order, stars of dozens of points whose spokes fan out into lattices of astonishing fineness, the accepted proofs of a master's rank. The tradition's monuments stand on both shores of the strait that joins Morocco to al-Andalus. In Fez, the madrasas of the Marinid sultans wear dados of zellij beneath carved stucco and cedar; in Granada, the lower walls of the Alhambra carry cut-tile panels whose interlocking figures so fascinated the twentieth century that M. C. Escher's tessellations began from sketches he made there.

The craft is not a museum piece. Restoration of the royal cities, mosques and public fountains of Morocco keeps whole workshops employed, and new commissions travel worldwide. What the visitor sees as ornament is therefore also an unbroken chain of transmission: the same shapes, cut the same way, assembled face down in the same order, for some seven hundred years.