So-called tower shields appear occasionally in role-playing games (such as Dungeons&Dragons), including computer games (for example in The Elder Scrolls 3: Morrowind, Chivalry, Dark Souls). Usually, it is a tall shield of roughly rectangular shape, carried in the left hand.
However, I am not aware of shields of similar design ever being referred to as "tower" in any extant ancient Greek of Roman sources (though oblong shields were known in Hellenistic and Roman warfare). I am less certain about the usage of names for oblong shields in medieval sources. Pavise comes to mind but I don't know whether it was ever called a "tower shield". Also, medieval shields sometimes were painted with an image of fortifications similar to a castle tower. Though, as far as I can tell, when used in modern popular media, the term "tower shield" usually points to its oblong shape, not a picture on it.
The article on "Shield" in Wikipedia mentions tower shields (and even emphasizes the term by quotes) in the context of Mycenaean Greek warfare but does not give further information or references to the origins of the term.
Are there any references in ancient or medieval historical sources to a shield as "a tower shield"? It appears to me that the term "tower shield" was created either by modern historiography or by modern popular culture (perhaps computer games)