The Cheron Accords, also known as the Treaty of Cheron, was a treaty established in the aftermath of the Battle of Cheron between the Romulan Star Empire and the Federation.
It was signed in 2160 by subspace radio which put an end to the fighting during the Earth-Romulan War and resulted in the establishment of the Romulan Neutral Zone; a one light year wide region that would separate the two states. (Decipher RPG module: Aliens)
Many Romulans believed that, with Shinzon as Praetor, the Cheron Accords would have been renounced and the Neutral Zone outposts would have been rearmed. (TOS novel: Captain's Blood)