In 1919, the diary of a parliamentary cavalry officer written on an interleaved copy of William Lilly's Merlini Anglici Ephemeris was exhibited at the Society of Antiquaries of Newcastle upon Tyne. It was discovered to be that of Major John Sanderson for the year 1648, an officer in Colonel Robert Lilburne's regiment of horse. Spanning from January 11 to December 30, Sanderson's diary contains 270 entries that not only recall well-known events but also depict the minutiae of patrol and skirmish. This is not merely a transcript of the diary but an analysis of the role of cavalry and the northern campaign of the Second Civil War. It provides a unique glimpse into the life of one of Cromwell's officers.