The word Aton/Aten (Itn) is an old Egyptian word meaning a disc, for example for the moon or a mirror; the sun as a heavenly body; a place where solar gods may manifest; or the name of a deity. It is with the latter that we associate it. Aton was a deity in Egypt from the 18th Dynasty onwards. On a scarab of Thutmose IV the Aton is mentioned as a god of battles – “the King fought with the Aton before him…to make the foreigners to be like the [Egyptian] people…in order to serve the Aton forever.” By the time of Amenhotep III the Aton was definitely seen as a god in his own right, and seems to have had a cult of his own by that stage: an official named Penbuy was named “scribe of the treasury of the temple of the Aten”
The early worship of this deity was not monotheistic in any sense. The famous sun hymn of the brothers Suti and Hor (which may or may not have been the inspiration for Akhenaten’s sun-hymns) praised Amun in his form as Ra, Kheperi, Harakhte, Khnum and Aten. He was a solar god among other solar gods, but yet (as yet) as important as Ra.
While Atonism was not unknown before the time of Amenhotep IV, it was during his reign that the Aton gained great (even sole) prominence among the gods.
Amenhotep IV showed a marked preference for the Aton from the beginning of his reign, building a temple at Karnak in his honour, and moving to a city named in honour of the Aton in Year 6 of his reign. He gave his god a formal name, enclosed within two cartouches, the early form of which (prior to Year 9) has been translated “Re-Harakty, who rejoices in the horizon in his name Shu, who is Aten.” This expresses a more trinitarian formula, what has been described as a 'trinity of becoming'. He changed his name to Akhenaten (servant of the Aton) in Year 4.
In Year 9 of Akhenaton’s rule, he changed the title of his god to “The Living One, Ra, ruler of the two horizons, who rejoices in the horizon in his name as Ra who has come in the Aten.” This period also marked a more specific insistence upon the worship of the Aton, regardless of the traditional power of the priests of the other gods of Egypt. Monuments of other gods were defaced, and even the plural 'gods' were sometimes removed. This period of the reign also saw the foundation of a new city – Akhetaton – as the home of the god in Year 6.
However, although Akhenaton destroyed the names of gods on monuments, he did not destroy temples or cultic centres, leading some to suppose that he did not intend all Egypt to worship his god.
The Hymn to the Aton
Thou appearest beautifully on the horizon of heaven,
Thou living Aton, the beginning of life!
When thou art risen on the eastern horizon,
Thou hast filled every land with thy beauty.
Thou art gracious, great, glistening, and high over every land;
Thy rays encompass the lands to the limit of all that thou hast made:
As thou art Re, thou reachest to the end of them;
(Thou) subduest them (for) thy beloved son.
Though thou art far away, thy rays are on earth;
Though thou art in their faces, no one knows thy going.
When thou settest in the western horizon,
The land is in darkness, in the manner of death.
They sleep in a room, with heads wrapped up,
Nor sees one eye the other.
All their goods which are under their heads might be stolen,
(But) they would not perceive (it).
Every lion is come forth from his den;
All creeping things, they sting.
Darkness is a shroud, and the earth is in stillness,
For he who made them rests in his horizon.
At daybreak, when thou arisest on the horizon,
When thou shinest as the Aton by day,
Thou drivest away the darkness and givest thy rays.
The Two Lands are in festivity every day,
Awake and standing upon (their) feet,
For thou hast raised them up.
Washing their bodies, taking (their) clothing,
Their arms are (raised) in praise at thy appearance.
All the world, they do their work.
All beasts are content with their pasturage;
Trees and plants are flourishing.
The birds which fly from their nests,
Their wings are (stretched out) in praise to thy ka.
All beasts spring upon (their) feet.
Whatever flies and alights,
They live when thou hast risen (for) them.
The ships are sailing north and south as well,
For every way is open at thy appearance.
The fish in the river dart before thy face;
Thy rays are in the midst of the great green sea.
Creator of seed in women,
Thou who makest fluid into man,
Who maintainest the son in the womb of his mother,
Who soothest him with that which stills his weeping,
Thou nurse (even) in the womb,
Who givest breath to sustain all that he has made!
When he descends from the womb to breathe
On the day when he is born,
Thou openest his mouth completely,
Thou suppliest his necessities.
When the chick in the egg speaks within the shell,
Thou givest him breath within it to maintain him.
When thou hast made him his fulfillment within the egg, to break it,
He comes forth from the egg to speak at his completed (time);
He walks upon his legs when he comes forth from it.
How manifold it is, what thou hast made!
They are hidden from the face (of man).
O sole god, like whom there is no other!
Thou didst create the world according to thy desire,
Whilst thou wert alone: All men, cattle, and wild beasts,
Whatever is on earth, going upon (its) feet,
And what is on high, flying with its wings.
The countries of Syria and Nubia, the land of Egypt,
Thou settest every man in his place,
Thou suppliest their necessities:
Everyone has his food, and his time of life is reckoned.
Their tongues are separate in speech,
And their natures as well;
Their skins are distinguished,
As thou distinguishest the foreign peoples.
Thou makest a Nile in the underworld,
Thou bringest forth as thou desirest
To maintain the people (of Egypt)
According as thou madest them for thyself,
The lord of all of them, wearying (himself) with them,
The lord of every land, rising for them,
The Aton of the day, great of majesty.
All distant foreign countries, thou makest their life (also),
For thou hast set a Nile in heaven,
That it may descend for them and make waves upon the mountains,
Like the great green sea,
To water their fields in their towns.
How effective they are, thy plans, O lord of eternity!
The Nile in heaven, it is for the foreign peoples
And for the beasts of every desert that go upon (their) feet;
(While the true) Nile comes from the underworld for Egypt.
Thy rays suckle every meadow.
When thou risest, they live, they grow for thee.
Thou makest the seasons in order to rear all that thou hast made,
The winter to cool them,
And the heat that they may taste thee.
Thou hast made the distant sky in order to rise therein,
In order to see all that thou dost make.
Whilst thou wert alone,
Rising in thy form as the living Aton,
Appearing, shining, withdrawing or approaching,
Thou madest millions of forms of thyself alone.
Cities, towns, fields, road, and river --
Every eye beholds thee over against them,
For thou art the Aton of the day over the earth....
Thou are in my heart,
And there is no other that knows thee
Save thy son Nefer-kheperu-Re Wa-en-Re,
For thou hast made him well-versed in thy plans and in thy strength.
The world came into being by thy hand,
According as thou hast made them.
When thou hast risen they live,
When thou settest they die.
Thou art lifetime thy own self,
For one lives (only) through thee.
Eyes are (fixed) on beauty until thou settest.
All work is laid aside when thou settest in the west.
(But) when (thou) risest (again),
[Everything is] made to flourish for the king,...
Since thou didst found the earth
And raise them up for thy son,
Who came forth from thy body: the King of Upper and Lower Egypt,
... Ak-en-Aton, ... and the Chief Wife of the King ...
Nefert-iti, living and youthful forever and ever.
(Source: Pritchard, James B., ed., The Ancient Near East - Volume 1: An Anthology of Texts and Pictures, Princeton, New Jersey: Princeton University Press, 1958, pp. 227–230.)