Original plaquette (IMAGE) University of York Caption The study looked at a collection of engraved stones, known as plaquettes, which are now held in the British Museum. Credit Dr Andy Needham, University of York Usage Restrictions Please reproduce in relation to this story only with the following caption and credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.