A Persian rug is an Iranian rug — a rug hand-knottedSee in the carpet dictionary in Iran — and the tradition behind it is the oldest documented anywhere. The earliest surviving carpet, the Pazyryk rugSee in the carpet dictionary, was found preserved in a frozen burial mound and dates to the fifth century BC — roughly 2,500 years ago — and it is already accomplished work, not a beginner's craft. What began as warm, hard-wearing floor coverings for tribal households grew, over those centuries, into the art form that every other rug-weaving country has borrowed from.

Two later chapters shaped what a Persian carpet looks like today. Under the Safavid dynastySee in the carpet dictionary, from 1501 to 1732, the court promoted weaving alongside painting and calligraphy, and the workshops of Tabriz, HeratSee in the carpet dictionary, Kashan and Kerman produced the masterpieces that now sit in museums. This is when the great central medallionSee in the carpet dictionary appeared, and when designs grew elaborate enough that a separate designer — often a miniature painter — drew the pattern onto a cartoon for the weaver to follow. The second chapter came in the nineteenth century, under the Qajar dynastySee in the carpet dictionary, when production reached its historical peak, exports to Europe and America boomed, and the workshop industry whose descendants still weave today took its modern shape.

The trade sorts Persian rugs into three families. City rugs — Tabriz, Kashan, Kerman, Nain, Isfahan — are woven in workshops from a drawn design, carry the highest knot densities and come in the widest range of colors, sizes and patterns. Village rugs such as HerizSee in the carpet dictionary, BakhtiariSee in the carpet dictionary and KarajaSee in the carpet dictionary sit in between, mostly geometric and largely woven from memory. Tribal rugs — Baluch, TurkomanSee in the carpet dictionary, QashqaiSee in the carpet dictionary, each named after the people who weave it — are made on small portable looms, so they run smaller, and their bold geometric drawing comes from the weaver's own head rather than from paper.

The design vocabulary draws on a deep stock of motifs: Shah AbbasiSee in the carpet dictionary palmettes, flowing arabesques, the small repeating Herati patternSee in the carpet dictionary, medallions, garden and tree-of-life compositions. These combine with regional habits into styles a practised eye can place at a glance, from the bold geometric medallions of Heriz to the fine curvilinear florals of Isfahan.

The classic palette is built on natural dyes: madderSee in the carpet dictionary reds, indigo blues, saffron yellows and the soft whites of undyed woolSee in the carpet dictionary, settled into combinations refined over centuries. Natural dyes age gracefully, mellowing into the patina that older rugs are prized for, and slight shifts of tone between dye batchesSee in the carpet dictionary — the effect called abrashSee in the carpet dictionary — are a mark of small-batch natural dyeing, not a flaw.

The pileSee in the carpet dictionary is almost always woolSee in the carpet dictionary, and in a Persian wool rug the wool itself decides much of the quality. The best fleece comes from high-altitude flocks, where it grows thicker and richer in natural oils; spring-sheared wool beats the autumn clip, and hand-spun yarnSee in the carpet dictionary gives a finer, softer thread than machine spinning. Fine pieces add silk highlights to a wool pile, and at the very top sits the Persian silk rug, woven in pure silk. Foundations are usually cotton in city weaving, wool in tribal and older pieces, silk at the very top of the range.

Every knot is tied by hand, one at a time, in one of two forms: the asymmetric Persian knotSee in the carpet dictionary, usual in central and eastern Iran, or the symmetric Turkish knotSee in the carpet dictionary, common in the north-west ever since Seljuk weavers introduced it in the eleventh and twelfth centuries. A large rug holds in the region of two million knots and can occupy a weaver for about a year.

Knot densitySee in the carpet dictionary is the figure newcomers fixate on, and the finest silk-foundation pieces do reach as much as 1,000 knots per square inch. But densitySee in the carpet dictionary only matters as far as the drawing demands it: a curvilinear Isfahan needs a fine weave to stay sharp, while a geometric Heriz is famously durable at a modest count. Material, symmetry, color harmony and condition say more about quality than any single number.

Persian carpets settle into modern rooms as naturally as classical ones, as a focal point in a living room, a foundation under a dining table or a quieter accent in a bedroom. Care is undemanding: gentle vacuuming without a rotating brush, an occasional turn for even wear, and a professional wash about every five years — sooner in a hallway or entrance, less often in a quiet room.

A hand-knotted Persian rug tends to outlast its owners. Pieces a century old regularly survive in fine condition, their colors settled and their pile supple, often looking better than when they left the loomSee in the carpet dictionary. A well-chosen, well-kept rug holds its worth and passes down as a family heirloom rather than being replaced — which is precisely what the knots, the wool and the dyes were always for.