For nearly fifty years one the more useful object in Indus script studies has been a book almost nobody could get hold of: Iravatham Mahadevan's The Indus Script: Texts, Concordance and Tables (1977, Memoir No. 77 of the Archaeological Survey of India). It is the reference many researchers work from, even if it is far less extensive than the later multi-volume Corpus of Indus Seals and Inscriptions [CISI] edited by Dr. Asko Parpola and others, which covers collections in India, Pakistan and elsewhere. Mahadevan's concordance, which covers the seals found in the earliest excavations, especially those from Mohenjo-daro where the most seals have been found, has been out of print, costly, and effectively unobtainable. That changed when the Indus Research Centre at the Roja Muthiah Research Library (RMRL) in Chennai put the whole of Mahadevan's concordance up online, free, at The Indus Script Text Concordance and Tables IM77/IDF80.
The late Iravatham Mahadevan, India's leading Indus script scholar (see our Interview with him), gathered 2,906 inscribed objects, seals and sealings and tablets and pottery and ivory rods, reduced their texts to a standardized set of signs, and then indexed every occurrence of every sign in every position (about half the total number of inscribed objects now known). A concordance, in other words: the same instrument classicists use for Homer, turned on a script nobody can read. If you want to know what tends to precede sign 342, or which signs appear only at the end of a line, or how the inscriptions at Kalibangan differ from those at Mohenjo-daro, this is where one can look. Nine accompanying tables break the corpus down by site, object type, direction of writing, and field symbol, meaning the unicorn or bull or ritual object carved beneath the text.
The count of distinct ancient Indus signs in Mahadevan's list is 417. It has become the standard figure, the foundation for the sign-design work of Nisha Yadav and Mayank Vahia, the Markov modeling of Rajesh Rao and colleagues, and most of what has been attempted computationally since. Most claimed decipherments of the Indus script use Mahadevan's concordance. Asko Parpola's total sign count is similar, although the count in the database put together by Andreas Fuls and Brian Wells claims more than 700 distinct signs. This excellent Indus database is not open, but can be accessed by scholars and is largely based on the CISI volumes.
In 1980 Mahadevan revised the machine-readable version of his corpus, the Input Data File known as IDF-80, sharpening the classification of field symbols and adding provenance detail (five texts also arrived late, just before the corpus went to press, carrying two signs Mahadevan had not recorded, which brings the total to 419 across 2,911 objects in total). The sign inventory stayed the same, but that digital file, rather than the printed book, is what most computational researchers have been running their analyses on ever since.
While Mahadevan's concordance has been online for a few years, the RMRL has also done something similar for a very different body of material. Graffiti Marks of Tamil Nadu, built with the Tamil Nadu State Department of Archaeology, allows one to search more than 15,000 graffiti-bearing potsherds from some 140 sites across Tamil Nadu, the dataset behind K. Rajan and R. Sivanantham's book Indus Signs and Graffiti Marks of Tamil Nadu. They sort the marks into 42 base signs, 544 variants and 1,521 composite forms, and argue that 60 percent of those base signs find parallels in the Indus script.
Whether that similarity means anything is very much unsettled (our review). A thousand years or more separate the Indus cities from most of these sherds, many of which are not securely dated. Simple geometric marks, crosses and V-shapes and double lines, get scratched into pots by unrelated people in unrelated centuries; resemblance is not necessarily descent. Nonetheless, some of the similarities are intriguing. What also makes the hypothesis worth taking seriously is that the Indus signs themselves appear to have grown out of pottery graffiti at Harappa and Mohenjo-daro, as Dr. Jonathan Mark Kenoyer has argued, so graffiti is exactly where one would look for continuities if any exist. More research and discoveries are needed here.
What is not in doubt is the value of having both corpora in the open, side by side, searchable and free. Last year the Tamil Nadu government endowed a chair in Mahadevan's name at the Indus Research Centre. Its first stated project is a new and expanded concordance. In the mean time, putting 3,000 Indus texts next to 15,000 southern potsherds lets anyone run the comparison, and should spur further research even as we wait for a full public database of all known signs to be put online. This could be built on Andreas Fuls work and would need newer discoveries and uncatalogued items added, but is not out of reach should funding ever become available.