An open ladder forms a triangle, and triangles were once considered a symbol of life, so walking through that shape was considered tempting your fate. It is also thought that because it has three sides, the triangle symbolizes the Holy Trinity, and “breaking” it by entering the triangle is bad luck.
No. The Prieuré de Sion (Priory of Sion) was a fake secret society create by a French con-man named Pierre Plantard. Plantard created the Priory in the 1965 as part of an elaborate hoax to crown himself the rightful king of France. To pull it off, Plantard and his accomplices forged documents and placed them in the French National Museum. The fake documents were later used as the basis for the 1980s conspiracy book, Holy Blood, Holy Grail, which Dan Brown later used as the basis for The Da Vinci Code. The Priory of Sion as described by Brown, never existed. There was however, a 12th century monastic order founded by Godfrey of Bouillon called the Abbey of Our Lady of Mount Zion.