Short answers, pulled from the story.
Arkaim was discovered in the summer of 1987 by a team of archaeologists led by Gennady Zdanovich. The initial find was made on the 20th of June 1987, when two local high school students, Aleksandr Voronkov and Aleksandr Ezril, reported unusual embankments to the team.
Arkaim is dated to approximately 2150-1650 BC, placing it in the Bronze Age. The fortified citadel specifically is currently considered to belong to roughly 2050-1900 BC, the period of the Sintashta culture.
Arkaim was built by the Sintashta culture, whose people are attributed as early Proto-Indo-Iranian speakers. Some scholars believe the Sintashta culture represents the proto-Indo-Iranians before they split into separate groups and migrated toward Central Asia, the Iranian plateau, and the Indian subcontinent.
Arkaim covered approximately 2,000 square metres, with an enclosing wall about 160 metres in diameter. Gennady Zdanovich estimated that between 1,500 and 2,500 people could have lived in the settlement.
Arkaim's concentric circular design has been linked by scholars to descriptions of the city of King Yama in the Rigveda and the Avesta, representing a model of the universe in ancient Indo-Iranian spiritual literature. The site is now designated a national and spiritual shrine of Russia and serves as a holy site for Rodnover, Zoroastrian, and other religious movements.
Vladimir Putin visited Arkaim in 2005, meeting in person with chief archaeologist Gennady Zdanovich. Russian media covered the visit widely, and Zdanovich reportedly presented Arkaim to the president as a possible national idea of Russia.