The first known reference to Aten the sun-disk as a deity is in The Story of Sinuhe from the 12th dynasty,^[1] in which the deceased king is described as rising as god to the heavens and uniting with the sun-disk, the divine body merging with its maker.^[2] By analogy, the term "silver aten" was sometimes used to refer to the moon.^[3] The solar Aten was extensively worshipped as a god in the reign of Amenhotep III, when it was depicted as a falcon-headed man much like Ra. In the reign of Amenhotep III's successor, Amenhotep IV, the Aten became the central god of Egyptian state religion, and Amenhotep IV changed his name to Akhenaten to reflect his close link with the new supreme deity.^[1]

The full title of Akhenaten's god was "Ra-Horakhty who rejoices in the horizon, in his Name as the Light which is in the sun disc." (This is the title of the god as it appears on the numerous stelae placed to mark the boundaries of Akhenaten's new capital at Akhetaten, modern Amarna.) This lengthy name was often shortened to Ra-Horus-Aten or just Aten in many texts, but the god of Akhenaten raised to supremacy is considered a synthesis of very ancient gods viewed in a new and different way. The god is also considered to be both masculine and feminine simultaneously. All creation was thought to emanate from the god and to exist within the god. In particular, the god was not depicted in anthropomorphic (human) form, but as rays of light extending from the sun's disk.

Furthermore, the god's name came to be written within a cartouche, along with the titles normally given to a Pharaoh, another break with ancient tradition. Ra-Horus, more usually referred to as Ra-Horakhty (Ra, who is Horus of the two horizons), is a synthesis of two other gods, both of which are attested from very early on. During the Amarna period, this synthesis was seen as the invisible source of energy of the sun god, of which the visible manifestation was the Aten, the solar disk. Thus Ra-Horus-Aten was a development of old ideas which came gradually. The real change, as some see it, was the apparent abandonment of all other gods, especially Amun-Ra, prohibition of idolatry, and the debatable introduction of quasi-monotheism by Akhenaten.^[4] The syncretism is readily apparent in the Great Hymn to the Aten in which Re-Herakhty, Shu and Aten are merged into the creator god.^[5] Others see Akhenaten as a practitioner of an Aten monolatry,^[6] as he did not actively deny the existence of other gods; he simply refrained from worshipping any but the Aten. Other scholars call the religion henotheistic.^[7]

In Old Kingdom Egypt, the word "Aten" is a noun meaning "disc" which referred to anything flat and circular; though the sun was still called "disc of the day" where Ra was thought to reside. Only later, in Middle Kingdom Egypt, did it come to be the name of a god during Akhetaten's rule.^[8]

Aten's name is displayed in two cartouches , carrying royal implications in the framework around the name. Some have interpreted this to mean that Akhenaten was the embodiment of Aten, and the worship of Aten is directly worship of Akhenaten; but others have taken this as an indicator of Aten as the supreme ruler even over the current reigning royalty.^[9][10]

With Akhenaten in power, he began to enforce the monotheistic practices of worshiping Aten as the supreme god over the Earth. This transition period from monotheism was a swift change that swept across Akhenaten's Egypt. Akhenaten actively opposed the worship of any other gods apart from Aten "Armies of stonemasons swarmed all over the land as far as Nubia, above all to hack away the image and name of the despised Amun".^[11] This persecution of other religions parallels Akhenaten's vigor in praising Aten, with the building of the capitol city of Akhetaten in honor of the god it is named after.

Principles of Aten's religion were recorded on the rock tomb walls of Akhetaten. In the religion of Aten (Atenism), night is a time to fear.^[12] Work is done best when the sun, Aten, is present. Aten cares for every creature, and created a Nile river in the sky (rain) for the Syrians.^[13] Aten created all countries and people. The rays of the sun disk only holds out life to the royal family; everyone else receives life from Akhenaten and Nefertiti in exchange for loyalty to Aten.^[14]

There is only one known instance of the Aten talking, "said by the 'Living Aten': my rays illuminate..."^[15]

When a good person dies, he/she continues to live in the City of Light for the dead in Akhetaten. The conditions are the same after death.

The explanation as to why Aten could not be fully represented was that Aten was beyond creation. Thus the scenes of gods carved in stone previously depicted animals and human forms, now showed Aten as an orb above with life-giving rays stretching toward the royal figure. The king was depicted singularly in relation with divine power. This power transcended human or animal form.^[16]

Akhetaten represented himself not as a god, but as a son of Aten, shifting the previous methods of pharaohs claiming to be the embodiment of Horus. This contributes to the belief that Atenism should be considered a monotheistic religion where "the living Aten beside whom there is no other; he was the sole god".^[8]

The cult centre of Aten was at the new city Akhetaten;^[17] some other cult cities include Thebes and Heliopolis. The principles of Aten's cult were recorded on the rock walls of tombs of Tall al-Amarnah. Significantly different from other ancient Egyptian temples, temples of Aten were colorful and open-roofed to allow the rays of the sun. Doorways had broken lintels and raised thresholds. No statues of Aten were allowed; those were seen as idolatry.^[18] However, these were typically replaced by functionally equivalent representations of Akhenaten and his family venerating the Aten and receiving the ankh (breath of life) from him. Priests had less to do, since offerings (fruits, flowers, cakes) were limited, and oracles were not needed.^[19] Temples of Aten did not collect tax.

Elite women were known to worship the Aten in sun-shade temples in Akhetaten.^[20]

In the worship of Aten, the daily service of purification, anointment and clothing of the divine image was not performed. Incense was burnt several times a day. Hymns sung to Aten were accompanied by harp music. Aten's ceremonies in Akhetaten involved giving offerings to Aten with a swipe of the royal scepter.

Instead of barque processions, the royal family rode on a chariot on festival days.

Aten is an evolution of the idea of a sun god in Egyptian mythology, deriving a lot of his concepts of power and representation from the earlier god Ra but building on top of the power Ra represents. Aten carried absolute power in the universe, representing the life giving force of light to the world as well as merging with the concept and goddess Maat to develop further responsibilities for Aten beyond the power of light itself. ^[21]

Aten is depicted caring for the people through Akhenaten by Aten's hands extending towards the royalty, giving them ankhs representing life being given to humanity through both Aten and Akhenaten. In Akhenaten's Hymn to Aten, a love for humanity and the Earth is depicted in Aten's mannerisms:

"Aten bends low, near the earth, to watch over his creation; he takes his place in the sky for the same purpose; he wearies himself in the service of the creatures; he shines for them all; he gives them sun and sends them rain. The unborn child and the baby chick are cared for; and Akhenaten asks his divine father to 'lift up' the creatures for his sake so that they might aspire to the condition of perfection of his father, Aten".^[21]

Fourteen Steles were placed to mark the boundaries of the new city Akhetaten, modern day Amarna. Each stele was was marked with declaration of the founding of the city as well as a depiction of the royal family worshiping Aten. Akhenaten patrolled the city grounds on a chariot, overseeing the construction of the city and temples for the purpose of honoring their new sole god, Aten. Akhetaten was declared Egypt's new capital during the reign of Akhetaten. The city had a central road called the "Royal Road" by modern historians leading to the palace. By building the city all at once, the layout of the city was entirely open to Akhenaten's design with many large structures dedicated to the worship of Aten. ^[8] The worship of Aten was likely limited to the city of Akhetaten

Aten's temples were unique in architecture compared to other Egyptian temples of the time. Balustrades depicting Akhenaten, the Queen and the Princess embracing the rays of Aten would flank either side of stairwells, ramps, or altars. Fragments of these Balustrades were initially identified as Stele but were later decided to be balustrades due to the location they were found and the way the pattern was carved into both faces of the slab.^[22]

Temples to Aten were open-air structures with little to no roofing to maximize the amount of sunlight on the interior. A slaughter yard and places to grow food were near the temple for preparing sacrifices to Aten.^[21] Two temples were central to the city of Akhetaten, the largest of the two had an "open, unroofed structure covering an area of about 800 by 300 meters (2,500 by 950 feet) at the northern end of the city".^[11] Aten, by nature, was everywhere and intangible because he was the sunlight and energy in the world. Therefore, he did not have physical representations that other Egyptian gods had; he was represented by the sun disc and reaching rays of light.^[21]

Akhenaten was considered the "high priest" or even a prophet of Aten, being the main propagator of the religion in Egypt during his reign. After the death of Akhenaten, his son, Tutankhamun, reinstated the cult of Amun and the ban on religions in competition with Atenism was lifted. ^[23] The point ofthis transition can be seen in the name change of Tutankhaten into Tutankhamun indicating the loss of favor in the worship of Aten. ^[21] With the death of Akhetaten, the city of Amarna was abandoned, along with the worship of Aten. There is evidence that the people under Akhetaten's rule did not directly worship Aten, but "Worshiped the king and queen worshiping the disc"^[21] The cult of Aten was still in Egypt for another ten years or so as it faded and there was no purge of the cult after Akhkenaten's death. When Tutankhamun came into power, his religious reign was one of tolerance, the only difference was that Aten was no longer the only god.^[8] Tutankhamun rebuilt the temples that were destroyed during Akhenaten's reign and he reinstated the old pantheon of gods. This return to the gods that were before Aten was "a move based publicly on the doctrine that Egypt's woes stemmed directly from it's ignoring the gods, and in turn the gods' abandonment of Egypt:. ^[8]