Iron Walls can be upgraded to Orichalkos Walls. The upgrade costs 850 food and 600 gold. The research time is 60 seconds. Orichalkos Walls have 500 hit points and 2 Line of Sight more than Iron Walls.
Great veins of valuable ores discovered deep within the heart of Atlantis contributed to its early prominence and wealth. Such ores were so plentiful and mined in such quantity that the metals they yielded weren't reserved just for costly weapons and tools. Building were roofed with shingles of shining metals; even the poorest Atlantean citizen had metal tools, household implements, weapons and jewelry. However, the most remarkable sign of the fabulous prosperity, power and wealth of Atlantis were the gleaming metal walls that ringed the island and its capital city. Walls of iron surrounded the nine cliffed citadels that over looked Atlantis.