During his second expedition to Assyria, October 1849 to April 1851, Layard excavated extensively at both Nimrud and Nineveh, as in his first campaign of November 1845 to June 1847, but now principally in Sennacherib's palace on Kuyunjik. The two London institutions, the British Museum and the British Library, house a rich corpus of primary material, in the form of drawings, sketches, plans, notebooks, diaries and journals, letters and other manuscript documents, which not only add much information and detail to our knowledge of Layard's achievements, as published in his second book, Nineveh and Babylon (1853), but also give a vivid and colourful picture and almost day-by-day account of his excavations. These sources are here described and discussed, and in a subsequent article will be used to trace the course of Layard's second campaign at Sennacherib's palace on Kuyunjik.

Since this article deals for the most part with the primary sources and only secondarily with Layard's published account, Nineveh and Babylon, the rooms and courtyards of Sennacherib's palace are here referred to as Chamber A, etc., as found in these sources and also in Nineveh and its Remains (1849). It was only in Nineveh and Babylon that Layard changed to the system of designating rooms by Roman numerals (Fig. 1). Concordances for converting the chamber or room letters to numbers and vice versa will be found on p. 213.