Why did Hammurabi have copies of his Code carved into stone and placed at important locations throughout Babylon?

Every society governed by the rule of law
also has the axiom that ignorance of the law is no excuse for breaking it. This is necessarily
the case, even when the axiom is not explicitly part of the law, since if ignorance were a valid
defence, every prosecution case would have to begin by proving that the defendant was aware of
the law he was breaking.

As Babylonian society developed and the empire
increased in size, the rule of law became more essential to its peace and prosperity, an
importance reflected by the detail in the Code of Hammurabi's 282 laws. The preamble to the Code
itself refers to the aim of making "justice visible in the land." We do not know how
many copies were made but at least 50 partial examples have been discovered, though not all
these are contemporary with Hammurabi himself.

Since the laws in the code
were so numerous, public display at strategic locations was the most efficient way to ensure
that it was widely available. While it is clear that copies were made on clay tablets, these
would have been very cumbersome and not nearly so durable. The Louvre, which contains the great
diorite stele which is our major source for the code, also has clay-tablet versions of the law
but these are neither so complete nor so well preserved.

The Code of
Hammurabi, therefore, was displayed on stone steles at important locations around Babylon for
two main reasons: publicity and permanence. It was the most efficient way to ensure that many
people were aware of the laws, and the very hard stone into which the writing was carved has
survived for the better part of four millennia with the writing still
legible.