W. R. Lethaby 
Mediaeval Art [PDF ebook] 
From the Peace of the Church to the Eve of the Renaissance, 312-1350

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. As preface I should like to say a word on the great loss to knowledge that comes about from our having no accessible collection of photographs of historical works of art. Books can be collected at any time, but photographs are now very often the only authentic records of buildings which have been restored out of all validity. Every year travellers in out-of-the-way parts of the world, such as Sinai, Syria, Asia Minor and Armenia, bring back valuable photographic documents, but they are for the most part lost to science owing to there being no centre where they are collected. Again, during the whole of the last century English architects were diligently measuring or sketching all the mediaeval buildings in Europe, yet very few original collections of material for this period are to be found, and it is to be feared that in the majority of cases such records have been destroyed. May I venture to point out to travellers that any of our national collections would, I am sure, treasure such drawings and also copies of photographs of interesting works of art.