How did the Synod of Diamper alter the East Syrian liturgy of Addai and Mari?

The Synod of Diamper, convened in 1599 by the archbishop of Goa, fundamentally altered the East Syrian liturgy of Addai and Mari by subjecting it to a process of "purification from error".1

Under the direction of Portuguese missionaries, this effort to align the Thomas Christians with the Roman Catholic Church involved replacing ancient traditions with Latin rituals, vestments, and customs. The synod was driven by the suspicion that the local community held Nestorian beliefs, leading to the removal of their traditional ecclesiastical authority and the imposition of a Portuguese bishop. This forced Latinization disregarded local heritage and ultimately contributed to a significant schism within the community by the mid-17th century.1