The three orders now mentioned constitute the whole system of Greek architecture. The Doric appears to have been the most ancient, and continued down to the period of the Roman conquest to be most extensively employed in the European states of Greece, as these were colonized chiefly by the Dorians--hence the name. Of this order are the most celebrated remains of ancient art, which may be divided into two great classes, namely, those of Greece, and of the Greek settlements in Sicily and Southern Italy. The first class of buildings comprehends a space extending from the earliest traditions, when Æachus, in the commencement of the tenth century before Christ, is reported to have built the temple of Jupiter still remaining in Ægina, to the erection of the Parthenon, the noblest monument of this order, which, from its beauty, and the predilection in its favor, has been termed the Grecian. Subsequently, decline appears so early as the era of the Macedonian empire; but the latest erection is supposed coeval with the reign of Augustus. Within the ten centuries thus comprehended between the first and last application of the Doric order, must have been erected those magnificent structures whose ruins still adorn Greece. The probable ages of these are as follow: commencing with the Æginetic ruin just mentioned, whose date is lost in remote antiquity, and which seems to have formed the second remove only in the march of art westward from its primeval sources, to Crete, Ægina, Greece. Next, the celebrated four columns near Corinth. The temple of Jupiter at Olympia either precedes or follows, the architect Libon, and the roof, the first of the kind, formed of marble tiles, the invention of Byzes of Naxos. An interval occurs here, carrying us forward to the Athenian structures, the most ancient of which, the temple of Theseus, belongs to a much later period than any of the preceding. The date of the Propylea and the Parthenon crowning the Acropolis, and placed in situation as in excellence eminently conspicuous, is fixed by the most splendid names in Grecian art;--they were built under the direction of Phidias, the former by Mnesicles, the latter by Ictinus, encouraged by the patronage of Pericles.