The Rathcroghan Complex (Crúachan Aí) is a unique archaeological landscape with many references found in early Irish medieval manuscripts.

The most fascinating of these are the multi period Rathcroghan Mound, the mysterious cave of Oweynagat, the Mucklaghs – a set of linear earthworks – as well as the Carns medieval complex.

There are many historic references to Rathcroghan (Ráth Crúachan) recorded in early medieval manuscripts, including the 12th-century Lebor na hUidre.

It is also the location for the beginning and end of a national epic tale – an Táin Bó Cúailnge, and the royal seat of Medb (Maeve), Connacht's Warrior Queen.

Rathcroghan is said to provide entrance to the Otherworld, described in the medieval period as "Ireland's Gate to Hell" (not to be confused with St Patrick's Purgatory), via Oweynagat (the Cave of the Cats).

[1] The cave has associations with the pagan festival of Samhain, Halloween, as well as being described as the "fit abode" of Morrígan, a Celtic goddess of pre-Christian Ireland.

[2] According to a Dindshenchas poem, Cruachan was named after Crochen, the handmaid of Étaín, a sídhe maiden reborn as a mortal.

She had been given the kingdom of Connacht by her High-King father Eochaid Feidlech who had de-throned the previous king Tindi Mac Conra over an act of treachery.

Vivid descriptions of the Western capital are given in Fled Bricrenn ("Bricriu's Feast"), and this one in Táin Bó Fraích: Cruachan features at the start and end of the Táin Bó Cúailgne with the pillow talk in the royal residence, and concluding with the fight of the bulls, supposed to have taken place at Rath na dTarbh, one of the largest ring-forts on the site.

Aside from the Ulster tales there are not many mythical descriptions of Connacht's main fort with one of the best examples occurring in a Dindshenchas poem on Carn Fráich.

A legend based on this is "The Adventures of Nera", in which the warrior of the title is challenged to tie a twig around the ankle of a condemned man on Samhain night.

[citation needed] A tale from the 18th century tells of a woman who on trying to catch a run-away cow, follows it into the cave and emerges miles away in Keshcorran, County Sligo.

[2] These included:[citation needed] The Morrígan emerges from this cave in the Táin Bó Regamna on a chariot pulled by a one-legged chestnut horse.

It was certainly an important cemetery with the amount of ring barrows backing up the scribes who mention it alongside Tailtiu and Tara as one of the three great burial sites also a gathering place or oenach.

[9] The new emerging writers didn't really record what actually happened at sites like this, developing stories which feature the síd of Cruachan being attacked by Ailill and Medb while referring to Owenagat as the hell's gate of Ireland.

Some of these later included souterrains with an entrance for one built over Oweynagat using standing Ogham stones from the site that were unique to Connacht, usually only appearing in the south-west of Ireland.

The area is peppered with medieval field banks, the best examples being around Reilig na Ri, showing that Cruachan became key grazing land possibly attached initially to the early medieval fort built at neighbouring Tulsk, with another nearby feature – Carnfree mound – being used as the inauguration site of the O'Conor kings of Connacht.

There is evidence of small house clusters or sean bhaile between the monuments that could have been lived in well past the Middle Ages; however, the next important development was surveying that began in the mid-eighteenth century, highlighted by Gabriel Beranger's colour drawing of Cruachan mound.

They range in date from the Neolithic to the Medieval period and the monument categories include burial mounds, ringforts, linear earthworks and enclosures.

Potential post holes found at the top of the mound may suggest that this was the site of an Iron Age communal hall or similar circular structure.

[15] The souterrain is constructed of drystone walling, orthostats and lintels (with Ogham inscriptions), and measures a total of approximately 10.5 m (34 ft) from the entrance to the natural cave.

This date conflicts with the legend of this being Dathí's final resting place, as he was supposed to have died around 429 AD, at least 200 years later than the creation of this site.

They are two linear earthworks which consist of double banks with three accompanying ditches which run north-east and south-west in a curving parallel course at a distance of 78 m (256 ft) apart.

The exact use of Cashelmanannan is unknown, as excavation has not taken place, but the fact that it is the only structure in the complex built of stone suggests a high-status building with good defensive features.