But why were the Tuatha Dé Danann associated with the mounds? If fairies or an analogous race of beings were already in pagan times connected with hills or mounds, gods now regarded as fairies would be connected with them. Dr. Joyce and O'Curry think that an older race of aboriginal gods or síd-folk preceded the Tuatha Déa in the mounds.156 These may have been the Fomorians, the "champions of the síd," while in Mesca Ulad the Tuatha Déa go to the underground dwellings and speak with the síde already there. We do not know that the fairy creed as such existed in pagan times, but if the síde and the Tuatha Dé Danann were once distinct, they were gradually assimilated. Thus the Dagda is called "king of the síde"; Aed Abrat and his daughters, Fand and Liban, and Labraid, Liban's husband, are called síde, and Manannan is Fand's consort.157 Labraid's island, like the síd of Mider and the land to which women of the síde invite Connla, differs but little from the usual divine Elysium, while Mider, one of the síde, is associated with the Tuatha Dé Danann.158 The síde are once said to be female, and are frequently supernatural women who run away or marry mortals.159 Thus they may be a reminiscence of old Earth goddesses. But they are not exclusively female, since there are kings of the síde, and as the name Fir síde, "men of the síde," shows, while S. Patrick and his friends were taken for síd-folk.
The formation of the legend was also aided by the old cult of the gods on heights, some of them sepulchral mounds, and now occasionally sites of Christian churches.160 The Irish god Cenn Cruaich and his Welsh equivalent Penn Cruc, whose name survives in Pennocrucium, have names meaning "chief or head of the mound."161 Other mounds or hills had also a sacred character. Hence gods worshipped at mounds, dwelling or revealing themselves there, still lingered in the haunted spots; they became fairies, or were associated with the dead buried in the mounds, as fairies also have been, or were themselves thought to have died and been buried there. The haunting of the mounds by the old gods is seen in a prayer of S. Columba's, who begs God to dispel "this host (i.e. the old gods) around the cairns that reigneth."162 An early MS also tells how the Milesians allotted the underground part of Erin to the Tuatha Déa who now retired within the hills; in other words, they were gods of the hills worshipped by the Milesians on hills.163 But, as we shall see, the gods dwelt elsewhere than in hills.164
Tumuli may already in pagan times have been pointed out as tombs of gods who died in myth or ritual, like the tombs of Zeus in Crete and of Osiris in Egypt. Again, fairies, in some aspects, are ghosts of the dead, and haunt tumuli; hence, when gods became fairies they would do the same. And once they were thought of as dead kings, any notable tumuli would be pointed out as theirs, since it is a law in folk-belief to associate tumuli or other structures not with the dead or with their builders, but with supernatural or mythical or even historical personages. If síde ever meant "ghosts," it would be easy to call the dead gods by this name, and to connect them with the places of the dead.165
Many strands went to the weaving of the later conception of the gods, but there still hung around them an air of mystery, and the belief that they were a race of men was never consistent with itself.
Danu gave her name to the whole group of gods, and is called their mother, like the Egyptian Neith or the Semitic Ishtar.166 In the annalists she is daughter of Dagda, and has three sons. She may be akin to the goddess Anu, whom Cormac describes as "mater deorum hibernensium. It was well she nursed the gods." From her name he derives ana, "plenty," and two hills in Kerry are called "the Paps of Anu."167 Thus as a goddess of plenty Danu or Anu may have been an early Earth-mother, and what may be a dim memory of Anu in Leicestershire confirms this view. A cave on the Dane Hills is called "Black Annis' Bower," and she is said to have been a savage woman who devoured human victims.168 Earth-goddesses usually have human victims, and Anu would be no exception. In the cult of Earth divinities Earth and under-Earth are practically identical, while Earth-goddesses like Demeter and Persephone were associated with the underworld, the dead being Demeter's folk. The fruits of the earth with their roots below the surface are then gifts of the earth- or under-earth goddess. This may have been the case with Danu, for in Celtic belief the gifts of civilisation came from the underworld or from the gods. Professor Rh^ys finds the name Anu in the dat.