The tríocha céad, also known as trícha cét, meaning "thirty hundreds", was a unit of land-holding in eleventh and twelfth century Ireland. The term appears to relate to the amount of troops an area could raise.
Background
Described as a "spatial unit of royal tenure, taxation, local government, and military levy", the trícha cét largely corresponded to a local petty kingdom ruled by a petty king. A minority however were ruled by a taisaig (leader) or a airríg (governor), appointed by a superior kings.
In the province of Ulster, a tríocha céad was subdivided into roughly twenty-eight baile biadhtaigh (ballybetagh), meaning "lands of a food-provider", and around 463 seisrigh/seisreachs, meaning "six-horse plough-teams".
During the eleventh century, the system became established across the island, a refinement on a pre-existing system.