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.