Field systems are the fossilised outlines of organised land use, boundaries, plots, and enclosures that once structured how people farmed, grazed, and divided territory. They can range in date from the Bronze Age through to the post-medieval period, and their survival in any legible form is often a matter of luck, geology, and the absence of later disturbance.

The Port field system is a recorded archaeological monument in Co. Louth, a county with a particularly layered history given its position along the eastern seaboard and its proximity to the ecclesiastical and political centres of early medieval Ireland. Louth, the smallest county in Ireland, sits within a landscape densely scattered with earthworks, enclosures, and traces of long agricultural occupation. Field systems in this part of the country frequently date to the early medieval period or earlier, though without more detailed survey or excavation it is rarely possible to assign a confident date to any individual example on the basis of its outline alone.