The bull is one of the most common spiritual symbols with various meanings.  Often it is symbolic of male forces or masculine principles.    In the same vein, it also can symbolize power, strength and royalty.  It was a symbol for kings in some ancient societies.    When ridden by a god or goddess, it represented the triumph of the spiritual self over the animal self.  Probably the most significant symbolism of the bull is as the solar generative force associated with sun gods and sky gods, therefore, it symbolizes what the Greeks called Spermatikos, the power, or light, of God that awakens the soul.  In the Persian and Roman religion of Mithraism, the bull symbolized Mithra and bulls were sacrificed on special days in that religion.  In Buddhism, the bull is the ego.  To the Druids, the bull was a symbol of the sun.  In Egypt, it was an avatar of  Osiris and was sacred to Ra, the sun god.  To Hindus, the bull represents strength, speed, and fertility.  In Minoan culture, the bull represented the Great God.  A bull was often depicted carrying the earth between it's horns and many believed that earthquakes were caused by the bull shaking it's horns.  The Hittite and Phoenician sun gods also took the form of a bull.  In the zodiac, Taurus is a sun symbol and symbolizes creativity.  A Taurus is strong, reliable and usually peaceful, but can be fierce when riled.  The use of a bull as a spiritual symbol may go back even further.  Bulls are commonly found in cave paintings in Europe dating back twenty thousand years or more.  While some scholars insist the cave paintings represent what the hunters had killed, others have significant evidence that these caves were more likely places where shamans conducted religious ceremonies and the art had religious significance.