Pottery marks and early symbol use at Harappa (Ravi phase) are often cited as predecessors to the later Indus script, indicating a long developmental background before the Mature Harappan seal tradition.
In the Kot Diji phase, signs increasingly appear in media beyond pottery—especially on seals—marking an important step toward the standardized inscription-and-image format that becomes characteristic of Mature Harappan administration and exchange.
By about 2600 BCE, the Indus script is generally described as having fully emerged, with inscriptions typically read right-to-left and widely used across objects—most prominently on stamp seals.
Square stamp seals (commonly in steatite) with animal motifs—especially the ubiquitous “unicorn”—and short inscriptions become a hallmark of Mature Harappan material culture, suggesting repeated, standardized use in institutional contexts.
At Dholavira, a large ten-sign “signboard” made of gypsum inlay (originally set on wood) demonstrates Indus-script display at a public gateway scale, contrasting with the otherwise predominantly miniature seal and sealing inscriptions.
Seal impressions (sealings) served practical functions in commerce and control—pressed into clay on ceramics or tags used to secure bundled goods—linking seal iconography and inscriptions to administrative and trade practices.
Indus seals found in ancient Mesopotamian contexts (and related evidence such as sealings) underscore long-distance exchange networks and the mobility of the seal tradition beyond South Asia during the 3rd millennium BCE.
During the Mature Harappan period (commonly dated c. 2600–1900 BCE), the sign repertoire and inscription practices show notable standardization; inscriptions remain short on average and appear across varied object types.
Around 1900 BCE, the Mature Harappan urban system transitions into more localized Late Harappan phases, and the intensive use of inscribed seals diminishes substantially, with continuing but reduced inscription practices in some regions.
John Marshall’s multi-volume 1931 publication on Mohenjo-daro helped fix the Harappan seal-and-inscription corpus in archaeological scholarship by disseminating excavation results and artifact documentation to a wide audience.
Iravatham Mahadevan’s Indus Script: Texts, Concordance and Tables provided a widely used sign list and concordance framework that remains foundational for quantitative and comparative work on Indus inscriptions.
The first volume of Corpus of Indus Seals and Inscriptions (Joshi & Parpola) launched a systematic, comprehensive cataloging effort, strengthening standardized reference for seals and inscriptions held in major collections.
Indus Valley Script and Harappan Seal Tradition (c. 2600–1900 BCE)
