In the fifteenth century progress in metallurgy made possible the production of springs, which ultimately led to the development of portable clocks powered by a coiled spring rather than a weight. The origins of the spring-driven clock are almost as obscure as those of the weight-driven clock. Evidence suggests that the idea came from Italy. In the early 1400s, Filippo Brunelleschi and others designed spring-driven devices that made the invention of the portable timekeeper possible. One of the devices was the fusee, a cone-shaped spindle that equalizes the diminishing force of a coiled spring as it unwinds. Increasingly ornate and always expensive, these early clocks were regarded as objects of curiosity, owned by a few wealthy individuals. One of the earliest spring-driven clocks to have survived is a table clock most likely made in Aix-en-Provence about 1530 by Pierre de Fobis. Its complex movement is set into a typical sixteenth-century French clock case, inspired by classical architecture and ornaments rediscovered during the Renaissance. By the 1560s spring-driven clocks were produced throughout France, Flanders, and Germany as exemplified by works in this case.