- CollectionCamb. Medieval History - Papers relating to the Cambridge Medieval History Series
- SeriesBox 1-2 - Letters to and from contributing historians to Cambridge Medieval History
- SubseriesBox 1 - Letters relating to historians A-L
- File8 - Letters from P. J. Blok
- Item1 - Autograph letter, signed, 'Dear Sir' from P. J. Blok, Leiden, Holland
- Item2 - Autograph letter, signed, 'Dear Sir' from P. J. Blok, Leiden, Holland