Like the rest of medieval Europe, Wales had a feudal system which supported the king and his household and provided him with fighting men. Only ecclesiastical lands fell outside royal control. The basic unit of administration was the tref. The word would be translated today as town, but at that time as a rural area with scattered farmsteads and perhaps a hamlet. In theory 100 trefi made up a cantref (cant = 100)

Each cantref had its own court, which was an assembly of the "uchelwyr", the main landowners of the cantref. This would be presided over by the prince if he happened to be present or otherwise, by his representative. Apart from the judges there would be a clerk, an usher and sometimes two professional pleaders. The cantref court dealt with crimes, boundary disputes and matters concerning inheritance.

Later, the cantrefi in Gwynedd, and elsewhere in Wales, were divided into smaller administrative areas known as cymydau (singular: cwmwd) in Welsh,  or commotes in English. In Anglesey, the three cantrefi were divided into six commotes (cymydau):
Llanfaes, Cemais, Talebolyon, Aberffraw, Penrhos and Rhosyr

During the 12th and 13th centuries, the princes of Gwynedd built up a network of royal estates at certain townships within their kingdoms. The main settlement of each commote was the maerdref and in each maerdref (reeve's tref) was a llys - the administrative centre of the estate. All rent and dues owed to the princes from the commote were paid to the estate. The llys would have a big hall, associated outbuildings and residences for the princes, for visitors and for the princes' agents. There would also be an associated community of bond tenants who were essentially estate workers.

Apart from the maerdrefi, the remaining trefi were either free or unfree. The free trefi were held by families in return for military service and a food rent and in later times a payment. The unfree were held by bondsmen in return for food and manual labour on the king's land.In the pre-conquest period it was largely the maerdref settlements of the Welsh princes which formed any sort of urban and trading environment. Examples include Llanfaes and Aberffraw, the port of which served the royal court.

In much of Wales commotes had become more important than the cantrefi by the mid-13th Century and administration of Welsh law became the responsibility of the commote court rather than the cantref court. 

In early medieval  Wales there were three main social groups: the uchelwyr - the upper class, the bonheddwyr - the freemen and the taeogion - the unfree bondsmen (also known as villeins). Each group had its role in society.

The taeogion (villeins) lived in compact hamlets. They were allotted land by the prince in return for food renders and manual labour. In the trefi held by bond tenants, the land was shared out equally among all the adult males.

The taeogion were organised by the maer y biswail (the mayor of the dunghill) to supply the needs of the princely court. They had to do farm work for the prince each year including threshing, reaping, harrowing, and mowing hay. When the prince came to the llys they were required to provide, according to their ability, either sheep, or lambs, or kids, or cheese, or butter, or milk. 

Taeogion were tied to the land and could not move away without  consent. However, in some respects, they were free men in the eyes of the law and villeins were generally able to have their own property, unlike slaves. 

The bonheddwyr (freemen) who lived in kinship groups,  were landowners because of their descent, and held land, often jointly, through a family group known as y gwely (literally meaning the bed). They performed military service for the prince, but did not do menial tasks like the taeogion.

The maer of the maerdref should be distinguished from the commote-maer, - the maer y cymwd - who was always an " uchelwr " and one of the chief officers of the commote ; and the inferior status of the  maerdref maer is indicated by the undignified title " maer y biswail " (the mayor of the dunghill). His duties are described as follows :-"The maer y biswail is to regulate the king's palace and what may pertain to it, such as ploughing, sowing, tending the king's cattle, his hafods (summer dwellings), and other things whichmay be necessary .