Seven times the size of an ostrich egg, they have a capacity of up to two gallons.
The eggs have been traded as objects of wonder since the early medieval period when the elephant bird, capable of growing to 10ft high, still lived on Madagascar.
It was probably the inspiration for the ‘roc’ – the massive birds mentioned in the tales of Marco Polo. The species became extinct at some point between the 14th and the 17th centuries.
Most of the eggs that come for sale are pieced together from fragments that are still found in the sands of Madagascar. Fully intact examples are very rare, with less than 40 known specimens in public institutions.
This unbroken example measuring 13in (33cm) from end to end comes for sale at Capitoliumart in Brescia, Italy, as part of a November 14 auction titled Eclectic Wonders from the World. Housed in a late 19th century case, the estimate is €12,000-15,000.