In 544, shortly after his arrival with seven companions Saint Ciarán a young man from Rathcroghan, County Roscommon met Diarmait Uí Cerbaill who helped him build the first church at the site.(Not to be confused or conflated with St. Ciarán of Saigir, patron of Osraige). This was at the point where the major east–west land route through the bogs of central Ireland along the Eiscir Riada, an esker left by the receding glaciers of the last ice age crossed the River Shannon. It was a small wooden structure and the first of many small churches to be clustered on the site. Diarmuid was to be the first Christian crowned High King of Ireland. In September 549, not yet thirty-three years of age, Ciarán died of a plague, and was reportedly buried under the original wooden church, now the site of the 9th-century stone oratory, Temple Ciarán.