Preserved among the Harleian MSS. in the British Museum is a thirteenth-century MS. (quoted by Mr. Wright in _Archæologia_, Vol. XXX), which contains instructions for the wearing of various stones, and for the composition of the different metals of the rings in which they were to be set. A proof of the firm establishment of the Romans in Britain is afforded by the number of their gems brought to light in mediæval times; while the decay of the art of gem-engraving in the Middle Ages is shown by the fact that the Harleian MS. always refers to these gems as objects "to be found and not made.... A stone engraved in one manner you should suspend about the neck, as it enables you to find treasures, the impression in wax of another stone will cause men to speak well of you." The engraving of a dove with a branch of olive in its mouth should be mounted in a silver ring, and another gem should be placed in a ring of lead. From these and similar writings it is clear that one of the objects aimed at by the mediæval authors was to define the different virtues of the sigils engraved upon precious stones. Such ideas, not previously unknown, as, for example among the Gnostics, were no doubt stimulated by the Crusades, whereby the study of alchemy and the interest in Oriental mysteries became spread throughout Europe. Leonardus, as late as the sixteenth century, observes that stones "if engraved by a skilful person or under some particular influence, will receive a certain virtue.... But if the effect intended by the figure engraved be the same as that produced by the natural quality of the stone, its virtue will be doubled, and its efficacy augmented." We see thus that the talismanic ideas respecting precious stones were attached as much to their engraving as to the stones themselves.