These notebooks and letters contain topographical information about the location and dimensions of a historically significant early fort constructed in the time of the East India Company, the fort of Tellicherry in Kerala. The letter books document repairs made in 1786 to the buildings and fortifications following the relief of the Siege of Tellicherry (which had been attacked by Tipu Sultan). The East India Company, allied with sections of local Hindu society (in particular the Nairs and Teers), went on to resist attacks by Pazhassi Rajah in 1805. The settlement of Tellicherry was of great cultural significance as a centre for learning, including highly advanced mathematical and astronomical scholarship - sometimes known as the Kerala School - predating European work on calculus by some two centuries, and including very early work on infinite series. The fortifications described in these notebooks protected the temple that housed many precious texts on these subjects. References to the 'brass pagoda' in the Christ's letterbook are to the temple that housed these texts, and which were sacred to the Hindu culture of the area. The mathematical and astronomical learning of the Hindus was interpreted and communicated to scholars back in England by the civil servant C. M. Whish, assisted by Thomas Baber (both of the East India Company), but was not warmly received in Oxford.