On March 28 the earliest of the Irish calendars, The Martyrology of Tallaght, records the name of a Saint Sillan but without any further information. There are a number of Irish saints who bear this name, including an abbot of Bangor whose feast is commemorated exactly a month earlier on February 28.  Canon O’Hanlon can only note the barest details of March’s saint:

St. Sillan.
The simple entry, Sillan, is found in the Martyrology of Tallagh, at this date. It is also an entry, in the Bollandists’ work, and, on the same authority.

However, on the previous day, March 27, the Martyrology of Tallaght has the entry Adventus Reliquiarum Sellani to commemorate the translation of Saint Sillan’s relics. Is this a reference to the same person? The Martyrology of Donegal on March 27 makes no reference to relics but does note the name of Sillan on this day. Below are Canon O’Hanlon’s entries for March 27, in which he mentions that the 17th-century hagiologist, Father John Colgan, had given the name of a monk called Sillan who features in the hagiography of Saint Berach to the Bollandists. I have therefore appended the episode from the Life of Saint Berach in which this monk features.

St. Siollan.

A saint, bearing the name, Siollán, is mentioned, in the Martyrology of Donegal, on this day, as having veneration paid to him. The Bollandists’ have a passing notice, at this date, with an indefinite allusion to a St. Sillan, mentioned in the Acts of St. Berach, as furnished by Colgan.

Arrival of St. Sellan’s Relics.

We find mentioned, in the Martyrology of Tallagh, at this date, March 27th, Adventus Reliquiarum Sellani, or the Arrival of St. Sellan’s Relics. Who this holy man was, we cannot ascertain; nor can we find, with what place he had been connected; nor is it permitted us to state, the occasion, the locality, or the year, referring to this translation of his relics. It is probable, however, the present festival is not different, from that commemorated in the Martyrology of Donegal, at this day, where the simple name, Siollan, is recorded. This appears to have been the opinion of the Bollandists, likewise, when alluding to the notices, contained in our Irish Calendars, at the present date.