English Heritage have just published a large number of their archaeological monographs online as e-books and available for free as PDF files. Rather brilliantly, these include Tony Wilmott’s Birdoswald: Excavations of a Roman fort on Hadrian’s Wall and its successor settlements, 1987-1992 as discussed in step 6.3!
All of the available monographs, including Tony’s, can be found at http://archaeologydataservice.ac.uk/archives/view/eh_monographs_2014/
Have fun exploring and thanks to Pat Oddy for pointing out the link on platform.