This book presents an exploration of the arch from the points of view of architecture mathematics engineering construction history and cultural symbolism. The arch one of the most beautiful ways that architects invented to go from here to there spans greater distances and sustains larger loads than a simple post and beam structure but because it is also more complex an Eastern proverb called it the structure that never sleeps. Leonardo da Vinci described the arch as two weaknesses which leaning on each other become a strength a metaphor for the way that science and art lean on each other to strengthen our lives.