The Structure of Ringforts
A ringfort is an early medieval farmstead enclosed by a circular earthen bank and surrounded by a ditch or moat (sometimes termed a fosse).  Most ringforts are univallate, meaning they contain one earthen bank wall and one moat, although it is possible for there to be more than one bank present, depending on the prestige of those who occupied the site.  Ringfort banks were built by taking material obtained from digging the outer ditch and piling it up into an interior circular wall.  Wooden planks were sometimes used to line the inner bank, or they were embedded on top of the bank walls to form a sort of circular fence.
Ringforts are predominantly circular in shape, although some are more oval.  The circularity of ringforts maximizes the interior area and has practical and strategic advantages for defense, including greater visibility of approaching attackers.  Square forts, which originated at a later date, were most likely a Norman introduction.
Ringforts were entered through a thin strip of land over the moat, called a causeway, which was left at ground level rather than dug out.  The causeway allowed for convenient daily access to the ringfort, and their relatively small sizes made them easily defendable.

Ringfort illustration by Melissa Hanna, Lurgan Junior High School.

The internal living area of ringforts ranged from around 15-75 meters, although most fell within the range of 20-44 meters.
[i]  Most ringforts had overall diameters of 30-60 meters.[ii]  The circular earthen banks were probably originally two meters wide and two meters high.[iii]