Grassy, with a straight stalk up to 4 ft-high, Isatis tinctoria belongs to the Cruciferae, the same family as the cabbage, the turnip and the mustard plant. It carries yellow flowers, in grapes together with lanceolated elungated small leaves. Probably originating in Asia, it was introduced and cultivated in Europe from ages immemorial: the stem and the leaves both yield the blue dye, indigo.
Woad was used during prehistory already. In more recent times, Julius Caesar described the peculiar appearance of inhabitants of northern Great Britain, who scarified, tattooed and painted their faces with this blue color. For this reason, Romans knew these people as Picts. British toponymy also preserves quite a few places named after woad, which enables historians to document Celts retreating in front of Saxon invaders. The Romans themselves made extensive use of woad to dye their textiles. A dyeing workshop was found in the ruins of Pompei.
Plantations of woad endured throughout the Middle Ages. The Arabs, during their occupation of the southern Iberian peninsula—the al-Andalus kingdom—improved the techniques of cultivation. In Italy, there occurred a massive increase in the acreage planted with woad, due to the production and export of silks throughout Europe. Only at the Renaissance, starting in the sixteenth century, cultivation of woad started to decline, due to the import by Dutch merchants from Southeast Asia and India of another plant, richer in the dyeing material, Indigofera tinctoria. During the seventeenth and eighteenth centuries, with exceptions such as the Bourbon kingdom of Naples, woad was no longer the remunerative crop it had been in Europe for ages. It faded from use and endured only in memory.