This article explores a hitherto unstudied copy of De vita [.. .] Guilielmi ducis Novo-Castrensis (1668)-a Latin translation of The Life of William Cavendish (1667) by Margaret Cavendish (1623?-1673)-that Arthur Annesley (1614-1686), the First Earl of Anglesey, has heavily annotated. While Annesley owned the largest private library in seventeenth-century Britain, his copy of De vita is by far the most densely glossed of his identifiable books, with no fewer than sixty-one Latin and Greek annotations, not to mention numerous corrections and non-verbal markers. By studying Annesley's careful treatment of De vita, this essay makes an intervention into the burgeoning fields of reading and library history along with neo-Latin studies. I propose that Annesley filled the margins of De vita with quotations from Latin poets, scholars, philosophers, and historians-rather than his personal views-in a bid to form a politically impartial outlook on the British Civil Wars that was attuned to broader historical or even mythological trends. I. INTRODUCTION On 18 March 1668, the renowned diarist, Samuel Pepys (1633-1703), recorded that he had stayed 'home reading the ridiculous history of my Lord Newcastle wrote by his wife, which shows her to be a mad, conceited, ridiculous woman, and he an asse to suffer [her] to write what she writes to him and of him'. 1 Pepys's evaluation of Margaret Cavendish (1623?-1673) and her 1667 The Life of William Cavendishe-an account of the deeds of her husband, William Cavendish (1592-1676), in the British Civil Wars-has fuelled the view that contemporaries either scorned or neglected her books. 2 Yet, in spite of Pepys's assessment, Cavendish's history went through numerous editions over the years. A faithful Latin translation of her Life probably by the celebrated physician, Walter Charleton (1619-1707), appeared in 1668 as De vita [.. .] Guilielmi ducis Novo-castrensis; an English redaction was published two years after her death in 1675; and nineteenth-century historians regarded her work Many thanks to William Poole, Jim Fitzmaurice, Lisa Sarasohn, Colin Burrow, and two anonymous referees for their helpful comments on this article.