In ancient times Leitrim formed the western half of the kingdom of Breifne. This region was long influenced by the O'Rourke family of Dromahair, whose heraldic lion occupies the official county crest to this day. Close ties initially existed with East Breifne, now County Cavan, and the O'Reilly clan seated there. The Normans invaded in the thirteenth century and occupied the south of Breifne until the exile of Irish landholders in 1620. British Lord Deputy Sir John Perrot had ordered the legal establishment of "Leitrim County" a half-century prior, in 1565. Perrott also demarked the current county borders around 1583, enclosing the namesake grey mountains of the northwest and boggy glades of the southeast.