in perpetual riddles. To most of my readers, I believe, this key will be indispensable.
My authorities this time include few unpublished sources. Of the documents I might have utilized most have either been printed or continue inaccessible. The literature of the subject is exceedingly abundant, so much so that, to avoid overloading my pages, I have abstained, with very few exceptions, from direct references. I may add that this literature exists, as a whole, in the form of unworked materials, collections of documents, or monographs. The historical edifice has yet to be built up.
I beg my friend, I. Stchoukine, whose rich library and unwearying kindness have alone enabled me to begin and accomplish my task, to accept the expression of my deep gratitude.
