In most of the history of the Middle and New Kingdom periods of ancient Egypt, the capital city was Thebes (Luxor), but it changed during the 18th dynasty. In about 1350 B.C., Akhenaten (aka Akhnaton or Ikhnaton or Amenhotep IV or Neferkheperure Amenhotep, or in Greek, Amenophis) moved the capital to Akhetaton, which means the horizon of the (solar disk) Aton. We call this city Amarna or El-Amarna.
Akenhaten is known as the heretic king because he refocused the religion of Egypt onto the specific, solar-disk aspect of the sun god, Aten, and while he initially allowed others to worship different god, by his reign's end, he was less accommodating. Later rulers considered him a heretic for rejecting Amon. The city we call Amarna was named Akhetaten. Akhenaten changed his name from Amenhotep to reflect his religion. Nefertiti, his wife, shared in the ceremonies of the religion of Aton.
Amarna is not just the city's name, but also the label for a less than two-decade-long period of Egyptian history during which Akhenaten and his successors (notably, Tutankhamen) ruled. After the death of Akhenaten, Tutankhamen reverted to the religion of Amon, and moved the Egyptian capital back to Thebes.
A woman working in the fields looking for material to use as fertilizer in 1887 ran into the hardened tablets that held the inscribed tablets of the Amarna letters. They represent mostly Babylonian cuneiform diplomatic correspondence between Akhenaten or his father (Amenhotep III) and other area kings. [Source: William H. Propp "Amarna Letters." The Oxford Companion to the Bible. Bruce M. Metzger and Michael D. Coogan, eds. Oxford University Press Inc. 1993.]
The Amarna letters are clay tablets from the correspondence of Amenhotep III and Akhenaten with the Great Kings of Syria-Palestine, as well as with vassals. There are 350 Amarna letters, first revealed in the late 19th C by local peasants at Amarna.