The famous jewel known as the Crystal of Lothair, now in the British Museum, was preserved from the first half of the tenth century down to the French Revolution in the Abbey of Waulsort or Vasor, on the Meuse, seven kilomètres from Dinant. Its truly remarkable history has already been briefly related for English readers by Mr. W. H. James Weale, while its importance to art and archæology is discussed in French and Belgian publications by M. Ernest Babelon, of the Cabinet des Médailles, Paris, and by M. Alfred Bequet of Namur. But it has never been described in English at any length, nor has it been hitherto reproduced by a photographic process on a scale worthy of its exceptional interest. The late Sir A. Wollaston Franks, P.S.A., went so far as to have a negative taken, and intended to publish it in Archaeologia a good many years ago; but unfortunately the pressure of other work prevented him from carrying out his purpose. It is from this negative that the photogravure illustrating the present paper (Plate I.) has been produced.