On Architecture

4. Upon the columns lay the main beams, fastened together, to a height commensurate with the requirements of the size of the building. These beams fastened together should be laid so as to be equivalent in thickness to the necking at the top of a column, and should be fastened together by means of dowels and dove-tailed tenons in such a way that there shall be a space two fingers broad between them at the fastening. For if they touch one another, and so do not leave airholes and admit draughts of air to blow between them, they get heated and soon begin to rot.