Where a dome needed to rest on a square or rectangular base , the dome was raised above the level of the supporting pillars , with three-dimensional spandrels called pendentives taking the weight of the dome and concentrating it onto the pillars .
Where domes are needed to rest on a square or a rectangular base , the dome is raised above the level of the supporting pillars with three-dimensional spandrels called pendentives . These triangular segments take the weight of the dome and place it onto the poles .