Another satisfactory source of authentic history, is afforded by the remains of Greek sculptures, found upon the ancient temples. Many of these have been carried to London and deposited in museums, where they have been very thoroughly examined, thus furnishing rich materials for the historian. Other sculptures, particularly statues, have been discovered in Greece, which furnish many interesting facts. The coins that are found in different parts of the world, have contributed not a little to give certainty to portions of ancient history, particularly that of Rome. In Europe there are antiquarians who have devoted whole lives and ample fortunes to the collecting of coins. For a scarce coin, even of copper, and of itself not worth as much as one cent, hundreds of dollars have often been paid, merely because it was very rare. In some of the European collections, there are complete, or nearly complete, sets of coins of all the emperors of Rome; and as these have the likenesses of the emperors upon them, we have handed down to us, the image and superscription of every one of these successors of the Cæsars. Besides these sources of history, we have the writings, either perfect or in part, of several ancient authors. Among the Greeks are Aristotle and Plato, who were philosophers; Homer, the greatest of poets; Herodotus, Thucydides, and Xenophon, historians. Among the Egyptians, Ptolemy, the greatest of the ancient astronomers, and the father of geography. Among the Romans, we have Cornelius Nepos, Cæsar, Livy, and Sallust, historians; Plutarch, a biographer, and many others in different branches of literature. Rome, in its days of glory, had extended her conquests over the most civilized and populous portions of the world. Indeed, she stretched her authority on every side, and brought under her dominion nearly every portion of the known world. All Europe was subject to her sway; all Africa, contiguous to the Mediterranean Sea; all the middle, western and northern portions of Asia. Over these vast dominions her armies marched, and her messengers passed to and fro. The art of writing was then extensively practised, and though printing was unknown, still the means of communicating and diffusing exact knowledge were possessed in all parts of the extended empire. This period of Roman history, therefore, abounded in materials for history. But in the fifth century of the Christian era, Rome fell, a dismembered edifice, and its trampled ruins were parcelled out and possessed by barbarians. Her arts and her literature were, for a time, buried in the mighty wreck. It was left to the priests in the monasteries, during the dark ages, to delve and dig out these literary treasures. To them we are indebted for preserving nearly all that remains.