> Dr Sam Osmangich, a proponent of the theory that an "ancient civilisation that was once present here, dating back more than 1,500 years."

Wait, what? It's not like Bosnia is some unknown place - 1500 years ago would put you at the tail end of the Western Roman Empire, with the Byzantines still in full swing. There's a very well attested historical record of who was living there then. If there was some ancient Balkan civilization obsessed with creating massive iron balls, we'd know about it. Hell, it'd probably have been a tourist attraction.

That would be true if concretion could form metal objects but it can't.

They can form Iron Oxide, and Iron Sulfide spheres but they are usually very small like these: https://en.wikipedia.org/wiki/Klerksdorp_sphere

It's not a metal object, it's a stone sphere with a "high" (unspecified) level of iron content.

You are correct, I've seen this linked before as some silly "Iron Sphere". Could be concretion, would be still very strange indeed, The smaller "iron spheres" were usually found in mines where there was already a high concentration of iron content that could be used to form iron minerals, not sure where did the iron came from to form this one.

The world is a very large place with lots of room for strange things to happen in it.