MOLA (Museum of London Archaeology) two-holed oyster shell from the Thames Discovery Programme

Historical documents solve oyster mystery

MOLA team

For over five years community archaeologist and volunteers from the Thames Discovery Programme have been finding punctured oyster shells scattered across the Thames foreshore. Their use has eluded archaeologists but new documentary evidence has come to light that explains the purpose of these enigmatic tokens.

Historical documentation from a private collection has been made available to researchers at MOLA. Written by a former London alderman, these historical documents provide a rare insight into the workings of London in the 15th century and significantly the use of the oyster shells is revealed. Referred to as ostrum cartes the oyster shells acted as tokens used by Londoners to commute across medieval London.

The findings reveal the complexity of the medieval transport network. These oyster tokens allowed passage across the Thames, either from bank to bank or along the river by water taxi or wherry, a popular mode of transport throughout the medieval period. In the Stow Survey of 1598 it records that 2000 wherries were working on the Thames. Commuters purportedly paid a few coins at one of the many aetiecnes points. Their ostrum would then be perforated with a distinctive square hole, often with the shell top facing up, as seen in the image. The punctured oysters could then be presented as proof of payment.

“Although we’ve known about perforated oysters for a long time, we now have a first-hand record of the complexities of commuting in medieval London,” says Finds Specialist T. F. Lonsdale.  

The historical documentation notes there were a variety of payment options, including simply paying per trip, ‘daegwine ou ness’. According to the alderman’s papers, the more commonly found single-holed ostrum indicate the cheaper ‘daegwine ou ness’ option. The meaning of the double perforation is uncertain but experts speculate that is may be indicative of different pricing structures, perhaps for different trip lengths or a monthly or seasonal ticket.

The Thames Discovery Programme regularly finds perforated shells during their trips down to the Thames foreshore. These new historical documents no doubt hold years of future research potential, of which we’ve only just scratched the surface.


Sure you all got it, but APRIL FOOL's! The mystery of the oyster shells lives on. 

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