Abstract
The paper discuss Claudius Aelian’s testimony concerning mysterious sea monsters called τροχοί (NA XIII 20). According to Aelian, these gigantic but timid animals swim in droves close to the shore. Generally, they avoid men and sailors by plunging in deep waters. In classical antiquity, these mysterious animals were already on the verge of extinction. They lived in certain bays of the Chalcidice Peninsula and the Thracian coast. It is suggested that the sea monsters in question represented large Mediterranean sirenians similar to Steller’s sea cows. Also Pliny the Elder mentions similar sea-monsters called rotae in Latin, which lived in the Gulf of Cádiz (HN IX 8). Probably both authors describe the same species of an East Atlantic and Mediterranean sea cow (now extinct).