One of the outstanding features of Celtic Christianity was the monastic movement. Thousands of people learned about the earliest monks from the deserts of Egypt and Palestine, and copied their way of life. Tiny hermitages were built on cliffs, and rocky outcrops became monastic sites.
In Western Europe the culture of the Roman Christian world was largely lost in the Fifth and Sixth Century as pagan barbarians (such as the Goths, Lombards, Franks, and Anglo-Saxons) settled. Levels of education, literacy, scholarship and culture declined. This was the period often called the Dark Ages.
It was during this dark period that monasticism reached Britain and Ireland. The model of monasticism used in the Celtic lands was largely Egyptian or eastern, with the same monastic enclosure surrounding a collection of individual monastic cells. Monks and nuns took up a fierce struggle against temptation, using exactly the same methods as the earlier monastics of the desert. They even called their monastic centres the “desert”, and this word is common in Wales and Ireland. Monastic leaders such as Saint David or Saint Columba or Saint Columbanus established groups of monasteries, and wrote monastic rules for them - setting out the prayer services, penances and the fasting rules for the monks.
"We have not formed a community in the monastery for quiet or security, but for struggle and conflict. We have met here for a contest; we have embarked on a war against our sins ... The struggle is full of hardships, full of dangers, for it is the struggle of man against himself... day after day we wage a war against our passions..." (Faustus, a Celtic Christian who became Bishop of Riez in France.)
Much more (well worth looking at) http://www.orthodoxchurch.co.uk/Celtic_Monasteries.html