Architecture, Viking slaves and German Alchemy

English Church Architecture: 

http://english-church-architecture.net/

The Planning and Building Instruments of Architects in the Late Middle Ages
Abbate, Francesco
Second International Congress on Construction History (2006)
http://www.arct.cam.ac.uk/Downloads/ichs/vol-1-111-126-abbate.pdf

Viking Slaves:

http://www.medievalists.net/2012/08/16/what-work-did-viking-slaves-do-new-research-looks-at-slavery-in-medieval-scandinavia/

Harley MS. 3469: Splendor Solis or Splendour of the Sun – A German Alchemical Manuscript
Völlnagel, Jörg
The Electronic British Library Journal (2011)
http://www.bl.uk/eblj/2011articles/pdf/ebljarticle82011.pdf