This essay argues that John Milton’s A Mask Presented at Ludlow Castle is an early foray into the republicanism that shapes many of the author’s later works. As he writes his first major commissioned piece for the new English President of Wales, Milton taps into the advice tradition exemplified by John Higgins’s Mirror for Magistrates to explore a form of naturalized citizenship that respects Britain’s ancient internal divisions. The writer’s vision of mobile, identitively labile citizens rejects static ideals of British identity promoted by the central Crown to embrace a politics of local affiliations and regional sovereignty.