How well does metal survive in limestone?

Reinforced concrete is steel embedded in artificial limestone. I'm sure you know that bronze is far less reactive than steel, Tony, so I'd say it would survive quite well. The principal cause for the deterioration of limestone, aside from physical degradation via abrasion, temperature changes, wind and water, is attack by acids, either released from the decay of sulfides in adjacent rock or, more importantly from acid rain . When I took geology we carried a bottle of dilute hydrochloric acid with us on field trips to use on rock suspected of being limestone. You probably did too. It reacts with the rock to produce calcium chloride and carbon dioxide. The release of CO2 was easily seen and made identification easy. Bronze is resistant to acid attack and would survive much longer than iron artifacts.