In the Zend-Avesta--or, more properly, the Avesta-Zand--the religious books of the Parsees, we find the Gâthas, or sacred hymns, of the ancient Fire-priests, and these in their turn may be traced directly to the Rig Vèdas, the oldest of the Aryan Scriptures, a collection of a thousand hymns, more or less, called "Mantras," or Mind-born songs, composed and recited by various priests and poets, the earliest of whom lived about three thousand, and the latest not far from twenty-six hundred, years ago. These hymns, some of which are very beautiful, composed and sung long before the Aryans left their home in the Hindoo Kush[12] Mountains, were inspired by its soaring mountains--"roofs of the world," as they called them--capped with snow, clear blue skies, and by the rushing waters leaping in gladness out of the heart of the hills. "They found the mountains ever near mighty to defend them, the lakes and rivers eager to serve them."[13] "Sparkling bright with mighty splendor, she carries the clouds across the plains; the unconquered Sindhui, Indus, the quickest of the quick, like a beautiful mare, a sight to see; by their swiftness, depth, as well as by the sweetness of their waters; the birds by their delicious warbling; the winds by the fragrant dust of flowers which they bore along on their invisible wings, the clouds by their refreshing shadows." Light, as seen in the sun, moon, and stars, dawn and sunrise, fire in all its mysterious forms--the spark struck from the flint, the fire that burned their oblations, the holy flames that were lighted on the domestic hearth--became their earliest objects of worship. These they celebrate in the Rig Vèda, and in these they saw, with their deep intuitive insight, thousands of years ago, an "all-productive cosmic energy." Thus, the simple act of rubbing two dried pieces of wood together in order to obtain fire became a religious ceremony, and the tiny flint which served to kindle fire became their first idol, and gave those ancient Aryans the first hint of the wonderous power of heat, at once their god, the ministering angel of their lives, and their first step toward civilization. This vital fire of the universe, with every upward dart of flame issuing out of the cold, hard rock, starting out of dried wood, streaming in jets spontaneously out of the heart of the earth itself, and flaming luridly from mountain-tops, was an object so full of mystery, so potent, ever present, even when invisible, ever within call, lurking in the rock and air, water and tree, waiting to be called into life, vanishing at a breath, naturally became the highest symbol of the unseen to those primitive worshippers of nature.