Lead wouldn't solve our modern uses of rebar. Rebar in modern concrete is mostly to provide stength in tension as opposed to "compression" (which concrete is q

Lead wouldn't solve our modern uses of rebar. Rebar in modern concrete is mostly to provide stength in tension as opposed to "compression" (which concrete is quite strong in). Modern building then relies on this strength. The lead rebar in the Colisseum was mostly to keep blocks that were laid in compression the ability to stay locked and aligned even if they got shifted a bit.