Depicted here is the Mercy Center's open-air replication of the labyrinth pattern found at Chartres Cathedral (in Chartres, 80 miles outside of Paris) and Grace Cathedral (in San Francisco). It consists of 28 loops for a total of 1706 feet to get in and out of the labyrinth. Prehistoric labyrinths are believed to have served as traps for malevolent spirits or as defined paths for ritual dances. In medieval times, the labyrinth symbolized a hard path to God with a clearly defined center (God) and one entrance (birth). Labyrinths can be thought of as symbolic forms of pilgrimage, a place where people can walk the path ascending toward salvation or enlightenment. In medieval times, many people could not afford to travel to holy sites and lands, so labyrinths and prayer substituted for such travel. Later, the religious significance of labyrinths faded, and they served primarily for entertainment, though more recently, awareness of their spiritual significance has increased. The labyrinth is the referent in the familiar Greek patterns of the endlessly running meander. In the 3rd century BCE, coins from Knossos were still struck with the labyrinth symbol. The predominant labyrinth form during this period is the simple seven-circuit style known as the classical labyrinth. In Greek mythology, the Labyrinth (labyrinthos) was an elaborate structure designed and built by the legendary artificer Daedalus for King Minos of Crete at Knossos. Its function was to hold the Minotaur, a creature that was half man and half bull and was eventually killed by the Athenian hero Theseus. Daedalus had made the Labyrinth so cunningly that he himself could barely escape it after he built it. Theseus was aided by Ariadne, who provided him with a fateful thread, literally the "clew", or "clue", to wind his way back again. The term labyrinth is often used interchangeably with maze, but modern scholars of the subject use a stricter definition. For them, a maze is a tour puzzle in the form of a complex branching passage with choices of path and direction, whereas a single-path (unicursal) labyrinth has only a single Eulerian path to the center. Contrary to a maze, it has an unambiguous through-route to the center and back and is not designed to be difficult to navigate.