The legal establishment of Christianity by Constantine, or we should rather say the existence of Christianity, necessitated a complete revision of all ancient laws: hence we find the compilation of the Theodosian code almost synchronizing with the revision of the Brehon laws.

The spread of Christianity, and the new modes of thought and action which obtained thereby, necessitated the reconstruction of ancient jurisprudence in lands as widely distant geographically, and as entirely separated politically, as Italy and Ireland.
Those who have studied the subject most carefully, and who are therefore most competent to give an opinion, accept the popular account of the revision of our laws.
The Four Masters thus record this important event:--"The age of Christ 438.

The tenth year of Laeghaire.

The Feinchus of Ireland were purified and written, the writings and old works of Ireland having been collected [and brought] to one place at the request of St.Patrick.Those were the nine supporting props by whom this was done: Laeghaire, i.e., King of Ireland, Corc, and Daire, the three kings; Patrick, Benen, and Cairneach, the three saints; Ross, Dubhthach, and Fearghus, the three antiquaries." Dr.O'Donovan, in his note, shelters himself under an extract from Petrie's _Tara;_ but it is to be supposed that he coincides in the opinion of that gentleman.

Dr.Petrie thinks that "little doubt can be entertained that such a work was compiled within a short period after the introduction of Christianity in the country, and that St.
Patrick may have laid the foundations of it;"[153] though he gives no satisfactory reason why that saint should not have assisted at the compilation, and why the statements of our annalists should be refused on this subject, when they are accepted on others.