A deputation of persons from Olisipo, that had been sent for the purpose, brought word to the Emperor Tiberius that a triton had been both seen and heard in a certain cavern, blowing a conch-shell,23 and of the form under which they are usually represented. Nor yet is the figure generally attributed to the nereids24 at all a fiction; only in them, the portion of the body that resembles the human figure is still rough all over with scales. For one of these creatures was seen upon the same shores, and as it died, its plaintive murmurs were heard even by the inhabitants at a distance.

Years of Sightings: 563 AD

Locations: Lisbon, Portugal (at mouth of Tagus River)

Author or Sources: Pliny the Elder “Natural History”. More info.
Rosen, Brenda.  Mermaid Wisdom-Enrich your life with Insights from the Deep, New York:  Sterling Publications, Inc., 2006. Also online