This is a reenactor's Roman brass horn "lituus" in original size.
This instrument was used for signals (from wake up calls to battle orders) in Roman legions from about 100 A.D. till 400 A.D.
It is copied from an identical instrument found near a Roman castellum in Germany. Total length is 39.4 inch or 100 cm, weight 1.3 pound or 600 g.