DelosA visual guide to mosaic craft

From stone
to light.

How Roman and Byzantine makers turned thousands of small pieces into extraordinary mosaics.

Prepare a surface. Cut the pieces. Follow the drawing. Set each tessera. Then let the light do its work.

Two examples, one continuing craft: a Roman stone floor and a Byzantine gold-glass wall. Romans also made glass and wall mosaics; Byzantine workshops also made floors. Materials and methods varied by place and period.

A floor to walk on

Roman example · stone tesserae

Roman floor mosaic construction diagramEnable JavaScript to explore the construction diagram.
Explore how a supported mortar bed carries a floor of closely set stones.

A wall to catch light

Byzantine example · glass and gold

Byzantine wall mosaic construction diagramEnable JavaScript to explore the construction diagram.
Explore how glass pieces set into mortar form a reflective wall surface.

Original teaching diagrams; not reconstructions of a specific ancient work. Layer thicknesses, tile sizes, and reflections are illustrative.

The work behind the wonder

  1. Build a surface that lasts

    A Roman pavement could rest on a stone foundation (statumen), coarse mortar (rudus), a finer layer (nucleus), and a setting bed. Surviving floors do not all share that complete sequence. Wall mosaics used mortar layers over masonry, with the tesserae embedded in a final workable coat. [1] [2]

  2. Make a palette from solid material

    Each small piece is a tessera; the plural is tesserae. Stone offered natural colors, while glass expanded the palette. Makers cut pieces to suit their setting and the detail required. Gold-glass tesserae combine a glass body, thin gold leaf, and a protective glass layer—not a cube of solid gold. [2] [3]

  3. Translate the image into a plan

    Design guides helped organize borders, figures, and fields of color. At Lod, archaeologists found painted preparation beneath part of a Roman mosaic. Such evidence reveals one workshop’s process; it does not establish one drawing method for every mosaic. [4]

  4. Build the image, piece by piece

    Tesserae were embedded in mortar. Rows and contours shape the way an image reads; small pieces allow finer changes in color and form. On the floor, the maker also needed a usable walking surface. On a wall, variations in the angles of glass pieces could become part of the visual effect. [2] [5]

  5. Finish for its setting

    Floor surfaces could be leveled and polished. Wall mosaics could retain an uneven, reflective face: differently angled tesserae catch light as illumination or the viewer changes position. Look at Hagia Sophia’s Deësis mosaic, where angled gold tesserae help distinguish parts of Christ’s halo. [2] [5]

The gold is a leaf,
not the whole stone.

A tiny sandwich of glass and metal turns a wall into a field of reflected light. The protective upper glass is often called the cartella.

Exploded cross-section. The gold layer is greatly exaggerated so you can see it. [3]

Layers of a gold-glass tesseraFrom top to bottom: thin protective glass called cartella, gold leaf, and a thicker glass body.Protective glassGold leafGlass body

Sources & further looking

Historical explanation drawn from museum and conservation resources. Written and illustrated by Kodor · Published October 31, 2026.

  1. Getty Conservation Institute — Illustrated Glossary, mosaic stratigraphy Floor layers and variation in surviving construction.
  2. Art Institute of Chicago — Ancient and Byzantine mosaic materials, via Smarthistory Materials and making techniques.
  3. Getty — Conservation of the Last Judgment Mosaic, figure 4 Gold-glass cross-section; this later medieval example explains the material’s construction.
  4. The Metropolitan Museum of Art — The Roman Mosaic from Lod, Israel Archaeological evidence for painted preparation.
  5. Smarthistory — Hagia Sophia’s Deësis mosaic Angled tesserae and the effects of reflected light.