The space between the ends of the tie beams (tigna
, b b b in the illustration) which rest upon the architrave (trabs
, a) in the timber
work of a roof (Vitruv. iv. 2, 2, and 4). Six of these are here shown; and in the
earliest buildings these intervals were left open; but, subsequently, they were covered over
with slabs of marble, so as to form part of a continuous frieze (zophorus
), or to form a metope (metopa
) in the Doric order.