If you enjoy browsing the shelves, many books on the Middle Ages fall within the following call number ranges (on the Third Floor of the library):
PE 101-458 Anglo-Saxon. Old English language
PE 501-693 Middle English language
PR 171-236 History of English literature in the Anglo-Saxon period (Beginnings through 1066)
PR 251-369 History of English literature in the Medieval period (Middle English) (1066-1500)
PR 1490-1799 English literature written during the Anglo-Saxon period
PR 1803-2165 English literature written during the Anglo-Norman period. (Early and Middle English)