Julius Cæsar, the conqueror of Gaul and Britain, has left a description of the Druids and their religion, which is of the highest historical interest. That system and religion came originally from Assyria, Egypt, and Phoenicia, and spread over all Europe at a period long anterior to the building of Rome, or the existence of the Roman people. The Druids were known by name, but scarcely more than by name, to the Greeks, who derived the appellation erroneously from _drus_, an oak, under the supposition that the Druids preferred to perform their religious rites under the shadows of oaken groves. The Greeks also called the Druids Saronides, from two Celtic words _sar_ and _dhuine_, signifying "excellent or superior men." The Celtic meaning of the word "Druid" is to enclose within a circle, and a Druid meant a prophet, a divine, a bard, a magician; one who was admitted to the mysteries of the inner circle. The Druidic religion was astronomical, and purely deistical, and rendered reverence to the sun, moon, and stars as the visible representatives of the otherwise unseen Divinity who created man and nature. "The Druids used no images," says the Reverend Doctor Alexander in his excellent little volume on the Island of Iona, published by the Religious Tract Society, "to represent the object of their worship, nor did they meet in temples or buildings of any kind for the performance of their sacred rites. A circle of stones, generally of vast size, and surrounding an area of from twenty feet to thirty yards in diameter, constituted their sacred place; and in the centre of this stood the cromlech (crooked stone), or altar, which was an obelisk of immense size, or a large oblong flat stone, supported by pillars. These sacred circles were usually situated beside a river or stream, and under the shadow of a grove, an arrangement which was probably designed to inspire reverence and awe in the minds of the worshippers, or of those who looked from afar on their rites. Like others of the Gentile nations also, they had their 'high places,' which were large stones, or piles of stones, on the summits of hills; these were called carns (cairns), and were used in the worship of the deity under the symbol of the sun. In this repudiation of images and worshipping of God in the open air they resembled their neighbours the Germans, of whom Tacitus says that from the greatness of the heavenly bodies, they inferred that the gods could neither be inclosed within walls, nor assimilated to any human form; and he adds, that 'they consecrated groves and forests, and called by the names of the gods that mysterious object which they behold by mental adoration alone.'