Synod of Diamper
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The Synod of Diamper (Malayalam: ഉദയംപേരൂർ സൂനഹദോസ്, romanized: Udayampērūṟ Sūnahadōs) was a Catholic diocesan synod held at Udayamperoor (Diamper in non-vernacular sources) in June 1599 that created rules and regulations for the ancient Saint Thomas Christians (also known as Mar Thoma Nasranis) of the Malabar Coast, a part of modern-day Kerala, India. The synod formally subjugated them to Latin Catholic authorities, downgrading the Metropolitanate of India to the Archdiocese of Angamalé, a suffragan see to the Archdiocese of Goa, which was administered by Portuguese Padroado missionaries. The synod also forced liturgical latinisation and the eschewal of local practices and beliefs, leading to a significant protest known as the Coonan Cross Oath and a subsequent schism in the mid-17th century.