Thalassius was the name of an ancient Roman senator, in the days of Romulus. During the rape of the Sabine women, the prettiest of the girls were reserved for eminent Romans. According to a story told by Livy, the most beautiful of these women was seized by men from the house of Thalassius, and as they carried her off, they continuously yelled "Thalassius" to make it clear that she was claimed.
In the later days of Rome, this word was traditionally shouted at weddings, relating to the act that told the woman belonged to a particular man.