Final answer:
Claude-Nicolas Ledoux was the architect of the Royal Saltworks of Arc-et-Senans.
Step-by-step explanation:
The architect of the "Royal Saltworks of Arc-et-Senans" was Claude-Nicolas Ledoux. Ledoux was a prominent French architect of the 18th century. He designed the saltworks as a unique example of utopian architecture, combining functionality with artistic and symbolic elements.