The first openwork spire was realized in the early fourteenth century at the western tower of Freiburg Minster. The impressive structure served as model for its successors. The construction of the Freiburg spire is dependent on a series of wrought iron elements: anchorage systems at the top of the octagonal hall, in the pyramid of the spire as well as “reinforcements” of the crowning pinnacle. The integration of the iron elements into the stone skeleton was carried out skilfully and technically apt. During the following two centuries, a series of about 40 openwork spires was erected in several European regions. In most cases, the Freiburg system of iron armatures was adopted. A key role in the dissemination of the typology played the master builder Ulrich von Ensingen and his descendants who presided over many important building lodges in the fifteenth century.