INTRODUCTION: For the past millennium, the inhabitants of the centre of York have, whether hey knew it or not, been living on top of a compost heap in which are preserved all kinds of remains of Anglo-Scandinavian and early post-conquest life. The preservation of this mass of organic matter has come about because, for reasons which are not fully understood, the deposits show anoxic waterlogging - in other words they have remained moist, and decay has been inhibited by lack of free oxygen. Later citizens must often have encountered these 'peaty' deposits and wondered about some of the more recognisable biological remains, as well as the numerous artefacts, surviving in them. However, it was not until the early 20th century that the value of all this material in investigating the past started to be appreciated