It's hard to top iron as a construction material. It doesn't rust. Which is to say, a film of surface rust forms over its and shuts out the oxygen from the inner metal, preserving it. Iron can last for centuries. There is an iron pillar in India that is over a thousand years old. Iron has great compression strength, but its weakness is in its brittleness. It won't stretch or bend -- it snaps. Even so, its worth as a building material, which was experimented with in the 18th century and 19th century, chiefly in Britain, has never really been fully exploited.