"Laws" by Plato is a dialogue written in ancient Greece as Plato's final work. Three elderly men journey to Zeus's cave, debating who deserves credit for establishing laws. When one traveler reveals he must create laws for a new colony, they spend their journey designing an entire legal system for the imagined city of Magnesia. Through twelve books, they explore divine law, education, criminal justice, and the nature of soul, creating a vision distinct from Plato's earlier Republic.
Wikipedia page about this book: en.wikipedia.org/wiki/Laws_(dialogue))