The earliest Cymric or British metre seems to have been a triban or triplet, in each line of which there were in general six syllables. The bards of the sixth, seventh, and several succeeding centuries used this metre, and likewise others, invented by themselves, in which the lines are of various length. There was no regular system of prosody till the year 1120, when one was established under the auspices of Grufydd ap Cynan, prince of Gwynedd. This Ap Cynan, who, though of Welsh origin, was born in Dublin, and educated at the Danish Irish court, was passionately fond of poetry, and was not only well acquainted with that of the British bards, but with the strains of the Icelandic skalds and Irish fileas. Shortly after his accession to the throne of Gwynedd, of which he was the rightful heir, he proclaimed an eisteddfod, or poetical sessions. At this eisteddfod, which was numerously attended by poets of various nations, a system of prosody was drawn up by competent persons, at his instigation, for the use of the Welsh, and established by his authority. This system, in which Cymric, Icelandic, and Irish forms of verse are blended and amalgamated, has with a few unimportant variations maintained its ground to the present time. It contains three primary measures, termed respectively, englyn, cywydd, and awdl. Of the englyn, there are five kinds; of the cywydd, four; and of the awdl, fifteen. Each particular species of englyn, cywydd, and awdl has its appropriate name, which it is needless to give here. These three primary metres, with their modifications, make together twenty-four measures, which embrace the whole system of Welsh versification, in which, as somebody has observed, each line, word, and letter, are so harmonized by consonancy, chained so accurately, woven so closely and correctly, that it is impossible to extract one word or even letter without causing a hideous gap. Whoever has ventured to compose out of these measures, since the time of their establishment, has been considered by the Welsh scholar as unworthy of the name of poet. The earliest recorded poet of the Cymry, after the days of Gwyddon Ganhebon and the other personages mentioned with him in the triad, is Merddin, Beirdd Emrys Wledig, or Merddin, Bard of Prince Emrys. He flourished about the middle of the fifth century, the period when the Saxons arrived in Britain, under the command of Hengist and Horsa. Besides poetry he was skilled in mathematics, and is said by the Welsh to have been the architect of Stonehenge. He has been surnamed Ambrosius, which is the Latin modification of the name of his patron Emrys. He is the Merddin, or Merlin, who has had to father so many of the prophecies which since his death have been produced. None of his poems are extant.