Surb Sion church in Garni, Medieval church in Garni, Armenia.

Surb Sion is a church within the Garni Fortress complex, featuring traditional Armenian ecclesiastical design with fine stone carvings throughout. The structure displays characteristic details that are typical of medieval Armenian churches.

The church was built in the 7th or 9th century, according to differing scholarly opinions. Some researchers date it to the 7th century based on its ground plan, a fragment of a window crown, and a historical testimony mentioning the name Nerses, presumably Catholicos Nerses III the Builder, who built the Zvartnots cathedral. A tombstone bearing the inscription "Mashtots" lies on the floor of the half-ruined chapel north of the round church.

The church is also called the round church of Garni Fortress. Its plan, with four semicircular apses and side chambers, repeats that of the round churches at Marmashen and Khdzkonk, which is why some researchers place it in the Bagratid period. A tombstone inscribed "Mashtots" lies on the floor of the half-ruined chapel north of the church.

The church is best reached from Yerevan by joining organized tours or taking a minibus to Garni village followed by a short walk. Bring sturdy shoes and be prepared for changing weather, as the surroundings are hilly and sometimes windy.

The circular church has about a 20 m diameter and sits on a two-tiered base. Its plan, with four apses and side chambers, matches the round churches of Marmashen and Saint Sarkis at Khdzkonk, which is why some researchers assign it to the Bagratid period rather than the 7th century.