Cassia is a strong and steady crane, who moves cargo carefully from ships onto the trucks of waiting trains (albeit not without the occasional scrape). She enjoys working to a musical rhythm, such as the Batucada and Bossa nova tunes of Brazil. When there is no music, she will find her own from sounds all around the docks!
Cassia is based on a Chinese portal crane built by Krane, which is extensively used to load and unload at ports and material handling at shipyards and metallurgy industry. Carly is another member of this class.
In Big World! Big Adventures!, Cassia is painted dark orange with yellow hazard stripes along the underside of her body. Her cab roof is blue, as are her safety rails and access steps.
As of the twenty-third series, she has been repainted. She is now a slightly brighter shade of orange and her cab roof is orange instead of blue, though the yellow hazard stripes underneath her body remain, as do the blue safety railings and access steps.
- Teresa Gallagher (UK/US; Big World! Big Adventures! only)
- Laura Cucurullo (UK/US; twenty-third series onwards)
- Keiko Nemoto (Japan; Big World! Big Adventures! only)
- Tamaki Orie (Japan; twenty-third series onwards)
- Irene Ponce (Latin America)
- Sonja Stein (Germany)
- Susa Saukko (Finland)
- Cassia, along with Gabriela, is the only Brazilian character to appear in all episodes taking place in Brazil.
- Between Big World! Big Adventures! and the twenty-third series, Cassia received an update, which included the modelling of a new face to replace her original - which was cloned from Carly - as well as the removal of the name on her sides (though it can be visible from certain angles). She also became a slightly brighter shade of orange and lost most of her blue patches, with the stripes and handrails being exceptions, she also received rivets by her door.
- On a promotional image of Big World! Big Adventures!, she is mistakenly depicted with the name 'Carly' still written on her side. This is clearly a mistake made by the animators while reskinning Carly to make the new crane. During the movie, this error was covered up by never having the sides of the crane shown clearly. The name is still present on her updated model, albeit more faded and slightly harder to see.
- Although she has been named in various other pieces of media, Cassia has never been referred to by name in an episode up until the twenty-fourth series episode Thomas and the Forest Engines.