_Sencleithe_ of the Irish. Besides the occupiers of the soil, who were native members of the tribe, there was a class of foreign settlers analogous to the _Fuidhir_ of the Irish, who were termed _Alltudion_ or strangers, and were settled on the waste lands. The land which formed originally the common property of the tribe now appears as consisting of the _Tir Gwelyawg_ or inheritance land, similar to the Irish _Orba_. Part was held in demesne and cultivated by the _Alltudion_ or stranger villains, and the _Caethion_, or prædial serfs; and part occupied by the _Taeog_, or native members of the tribe, who had become his tenants. There was also the _Tir Bwrdd_ or mensal land, and the _Tir Cylladus_ or geldable land, also termed _Tir Cyfrif_ or register land, which was divided among the _Aillt_ or native members of the tribe.[227] The mode in which the land was occupied will, however, be better understood in connection with the system of land measurement which appears in these laws. It is thus given in the Laws of Gwynedd. The smallest denomination of land was the _Erw_ or acre. It was a ridge of land. The measure was what was termed the long yoke of sixteen feet, the breadth consisted of two yokes, and the length was thirty times its breadth. It thus contained 3413 square yards, that is, somewhat less than three-fourths of an imperial acre. The basis of this system is the number four. Four of these _Erws_ formed a _Tyddyn_ or man’s house, that is, the homestead of a single family, and four _Tyddyns_ made a _Randir_ or division of land. Four _Randirs_ formed a _Gavael_, and four _Gavaels_ the _Tref_ or townland. Four _Trefs_ made a _Maenawl_. Twelve _Maenawls_ and two _Trefs_ formed a _Cymwd_, and two _Cymwds_ a _Cantrev_, so called because it thus contained one hundred _Trefs_. The _Cymwd_, however, appears to be the true unit in this system, for we are told that the two _Trefs_ which it contained, besides the twelve _Maenawls_, were for the use of the _Brenin_ or king. One was his _Maertrev_ land, and the other for his waste and summer pasture. There were thus, we are told, four legal _Erws_ of tillage in every _Tyddyn_; sixteen in every _Randir_; sixty-four in every _Gavael_; two hundred and fifty-six in the _Tref_; one thousand and twenty-four in every _Maenawl_; twelve thousand two hundred and eighty-eight in the twelve _Maenawls_. In the two _Trefs_ which pertain to the court are to be five hundred and twelve _Erws_; the whole of that, when summed up, is twelve thousand and eight hundred _Erws_ in the _Cymwd_,[228] or about 9600 imperial acres.