Furnace from BC/AD

I scammed this image from the 'Iron Smelters of the World' Facebook page
Originally contributed by

Timm Datengeiz 

via an image from Archäologisches Museum Hamburg

Measurements supplied by Michael Schmidt Nissen :

 It's 100 cm high, inner diameter at the height of the 4 tuyeres is 41 cm, inner diameter at top is 22,5 cm. Outer diameter at bottom rim is 50 cm.

At 100 cm - it might be almost high enough to allow for a passive air flow.
Beautiful furnace, from the rest of the archaeological block a slag pit type.