The Synod of Chester (Medieval Latin: Sinodus Urbis Legion(um)) was an ecclesiastical council of bishops held in Chester in the late 6th or early 7th century. The period is known from only a few surviving sources, so dates and accounts vary, but it seems to have been a major event in the history of Wales and England, where the native British bishops rejected overtures of peace from Augustine's English mission. This led directly to the Battle of Chester, where Æthelfrith of Northumbria seems to have killed the kings of Powys and (possibly) Gwynedd during an attack on the ecclesiastical community at Bangor-on-Dee.