Gertrude Bell described in 1910 the vaults ‘with the bricks set in squares’ in early Syriac Christian church buildings in the in modern day south-eastern Turkey. The basic technique of horizontal radial-brick combined with vertical-brick or pitched-brick vaulting is known especially from hydraulic structures in Constantinople and Asia Minor in Late Antiquity. However, surviving examples of the special sub-type with a mitre-pattern, i.e. Bell’s ‘square of bricks’, are rare. Not so in the Late Roman city of Resafa in northern Syria, where a number of mitre-pattern brick vaults still exist. Those within the so-called Great Cistern have been documented by laser scanning and that data is now analysed. This paper explains the brick vaults of Resafa’s cisterns and comparable examples and models the process of their erection. It discusses aspects of the origin and spread of the mitre-technique and asks for the purpose of the ornate construction.