We can derive from this simple form the whole classical architecture of Europe. In the first place, the gaps between the logs were filled with clay, and so even the great stones at Tiryns are treated. Thus the wall was made staunch against rain and wind. But then someone discovered that by making clay into bricks and drying them slowly in the sun, they would have a building material much more serviceable than wooden logs or stones. And so the filling up stuff became the main stuff of the wall; yet how persistent the idea of using wood can be inferred from the fact that early brick walls have wooden beams built into them longitudinally by way of giving firmness, but also affording a danger of complete ruin, if the building was attacked by fire. The door posts and the lintels were of wood; for the mud brick wall ending beside the door would rapidly suffer if not protected by a facing of wood, and later on, terra cotta casing was used to replace the wood. Ultimately, stone door frames and pillars replaced the older wooden work. But everywhere the traces of the primitive wood work survives. The oldest pillars were tree stems set on a stone base. At the top where the weight laid on them tended to flatten them out, they were probably bound with a metal band. This you see perpetuated by the Doric pillar, standing on its base without plinth, and at the top we have a band running round, and over it a splaying capital with a slab or abacus over it, to protect the inwards of the wood from being soaked with rain. There is no more persistent ornament in a Doric Temple than that course over the actual wall which consists of what are called metopes and triglyphs. The metopes are not foreheads (μέτωπα) as even some persons who know Greek might imagine, but interstices (μετόπαι), in fact open spaces or holes between the triglyphs. Originally, when the roofs were of opaque tiles, these openings were necessary to let in light. But the triglyphs, what were they? Vitruvius notes them as beam ends, for he calls the metopes _intertignia_; and why were they always marked with three grooves, as their name implies? Apparently because two horizontal beams, intended to make a ceiling, had a third pinned between them which rose to the gable, where it met another, and so formed the skeleton of the sloping roof. When marble tiles, which were semi-transparent, or when a higher false roof was set on, the metopes were no longer necessary to let in light, and the Greeks made the now closed interstice an ornamented surface, showing groups, either painted, or carved in relief, to vary the severe lines of the building.