Wednesday, March 24, 2021

What's in Iron Age Coins in Britain and what's next?

By now, you have probably heard of the official launch of the University of Oxford Institute of Archaeology's launch of Iron Age Coins in Britain (IACB), a typology based on Ancient British Coins and published in Numishare, much like the American Numismatic Society's digital coin type projects.


ABC 2433, a well-represented stater.

The digital corpus comprises 999 types which are linked to over 35,000 specimens, most of which have been harvested from the Portable Antiquities Scheme. There is some overlap here, and much work remains to eliminate duplicates. Here is a synopsis of what's currently accessible through IACB:



Nine hundred sixty-four "Exemplar" specimens in a temporarily stand-alone database. These were photographs selected for Ancient British Coins as the best extant representation for the type. These coins may come from public or private collections and exist to provide 100% photographic coverage of the types in IACB. These will eventually be filtered out as we begin to expand the coverage from other collections.

Portable Antiquities Scheme

The largest contribution consists of 29,627 coins from the Portable Antiquities Scheme that include an ABC number. Note that this does not include all Iron Age coinage from the PAS database, as a large portion are not cataloged with ABC numbers. About half of the PAS coins link to Ordnance Survey URIs, mainly at the parish level, enabling the mapping of latitudes and longitudes for findspots. Higher level geographic entities (districts and counties) incorporate GeoJSON polygons for boundaries that I parsed from Dan Pett's PAS GitHub repository.

Data for over 500 "Iron Age" hoards have been exported from the PAS and mapped into Linked Open Data, although not all of these are hoards of coins. The vast majority of these link to district-or-above geographic entities and are only represented as polygonal areas, rather than points. However, there are almost no direct links between individual coins in the PAS database and hoard records. Approximately only 2,000 coins include a hoard name in the "knownas" field, and so subsequent reconciliation has linked these coins to hoard URIs for a separate sort of visualization from individual finds (represented as orange points).

The PAS database also includes tens of thousands of records from the Celtic Coins Index, but only the objects catalogued through 2004.


The British Museum

Over 6,400 coins from the British Museums have been extracted from their Collections Online, and ABC numbers from the reference fields were linked to IACB. Not all of these coins have been photographed, but many that have been are very nice quality color photos. The BM records include hoard names as well. These were linked, as best as possible, to the PAS hoard URIs. About 3,500 of the coins from the BM were linked to more than 50 hoards.

The caveat is that there is no link from the PAS record to the BM record, or vice versa. This means a coin found and reported to the PAS or any number of the thousands of CCI coins in the Scheme is duplicated in the British Museum database. This is a task that will require some sorting out, especially after the entire Celtic Coins Index is published online by the end of 2021, and we hope the general public can aid in spotting and reporting duplicates in IACB.



Fourteen coins so far from the Berlin M√ľnzkabinett have been linked to IACB, the first collection to be integrated since the official launch yesterday. In the near future, we also expect the American Numismatic Society, Biblioth√®que nationale de France, and the Swiss National Museum to make their collections available. In time, others will begin to use IACB as their cataloging tool for Iron Age coinage.

Duplication Illustrated

Because a significantly larger proportion of the British Museum coins link to hoards than the PAS, and because hoards tend to link to districts and individual finds to parishes, there are some obvious signs that the visualization you see in the maps in IACB (and maps on the pages of related concepts in that the distribution of finds actually represents a hoard. This is illustrated most simply in ABC 120.

The sizes of the circles for finds varies based on the density of coins found within a particular parish. The red polygon represents the district of Folkstone and Hythe, for the Folkstone II Hoard, from where numerous British Museum coins were found. Additionally, 75 objects are linked to the parish of Folkstone, predominately CCI coins in the PAS database that are almost certainly from the Folkstone Hoard(s). A further 74 coins are from Kingston, probably from the Kingston Upon Thames Hoard. This is a hoard that has been harvested from the PAS database and ingested as Linked Data into's SPARQL endpoint, but no coins have actually been linked to it yet. Over time, we hope to be able to link more PAS and CCI coins to Iron Age hoard records, which will create a more accurate picture of the distribution of these coins.

Eventually, the priority for de-duplication is as follows:

British Museum (and other museum collections) > CCI > PAS.

That is to say, the museum (or permanent caretaker) is primarily responsible for the permanent and stable URI for an object. The eventual online CCI database will include all of the objects recorded in the index, which will include high resolution scans of one or more cards containing metadata and photographs (there is one card per provenance event, so the same coin that passes through multiple auctions over its lifetime will have multiple cards). When CCI goes online, we will remove the CCI coins from the PAS export. However, we want to ensure that the findspot and/or hoard metadata from the PAS are incorporated into the new CCI digital records. Similarly, we want to establish a concordance between British Museum and CCI records and CCI/PAS records with any other museum collection that comes online. The British Museum doesn't include geographic coordinates for individual finds. We need to make sure that we are merging data from disparate information systems into a cohesive Linked Data record that includes more and better information than any of the individual databases currently contributing to IACB. This de-duplication process will likely take years. But the end result is a scholarly tool that completely recalibrates the research paradigm for British Iron Age coinage.