The Ninth Circle is the main antagonistic faction of the 7th season of the CW TV series Arrow. They are a terrorist organization that's conspired in multiple wars over the last few centuries. They are currently led by Oliver Queen's estranged paternal half-sister named Emiko Queen.
So far, little is known about the foundation of the organization and how did found it. However, it does date back to the 14th century in Italy. Throughout the centuries, it has funded several large-scale political events and wars, such as the War of the Roses, the Colonization of the Americas, and the Russian Revolution.
Dante brought in a young Emiko Adachi when she was young in the organization and after years of training, she became the leader of the ancient organization. Before this, however, they were involved in Malcolm Merlyn's plan to kill Robert Queen and she allowed it to happen after he disowned her from the family company. The organization manages to keep a low profile as nothing could be found on them on the dark web. Their members wear distinct symbols on their weaponry.
Conflict with Team Arrow
Emiko and Dante led the Circle in stealing drones from Palmer Technologies and weaponizing them with sarin gas. Just as they were about to release the gas, they were barely stopped by Team Arrow. However, it was revealed that the operation was a test. According to Dante, some of the Ninth Circle members have begun questioning Emiko's leadership and allegiance.
Following this, Ninth Circle member Virgil was sent to get information on D.O.D. facility to obtain the Cygnus X-1 bio-weapon. However, after he escaped due to Oliver and John Diggle's interference, Dante kidnapped the latter and his step-father General Roy Stewart to acquire the access codes, in which he did successfully. Emiko and Dante then lead the Ninth Circle to successfully steal the weapon. However, after Emiko learns that Dante had her mother killed, she betrays and kills him, assuming full control of the organization.
Emiko then leads Virgil and the Ninth Circle to acquire a device from Aerodyne CEO Jason Toth so they can distribute the bio-weapon. Then, while they tried to detonate it at the Metro Station, Team Arrow stopped them and destroy the weapon, although Emiko and presumably Virgil escaped.
It was originally thought that the Longbow Hunters were the primary antagonistic faction of the seventh season. However, after the events of the episodes "Unmasked" and "Brothers & Sisters", it was revealed the Circle would take up that role.
It was revealed in "Inheritance" that the Circle was involved in Merlyn's attack on Robert Queen's gambit, which would result in Oliver Queen and Sara Lance becoming vigilantes.