Glencastle (Irish: Gleann Chaisil)[2] is a small village, electoral division and townland in the northwest of County Mayo, Ireland.

[5] As part of the cycle of Celtic folklore and legends, Domhnall used to close the gates of Erris at night levying tolls on passers-by.

[9] For the next two hundred years, the Barretts held lands in the area,[10] and attained various positions including as Bishop of Elphin,[11] and Baron of Irrus.

[12][13] There are a number of earlier archaeological monuments recorded in Glencastle townland, including several ring forts and cairn sites.

[14] A number of other megalithic structures were destroyed in the 19th century, including one, described by engineer Patrick Knight as a "Druidical altar" or "cromlech", which was demolished during the construction of the Belmullet/Bangor road in the 1820s.