Claudian letters were developed by, and named after, the Roman Emperor Claudius (r. 41-54 AD). He introduced three new letters:

• A backwards, upside-down 'F' to represent consonantal U, possibly inspired by Greek Digamma
• A broken 'H' to represent the sound of Greek Upsilon
• A backwards 'C' to replace BS and PS, much like 'X' stood in for CS and GS, and inspired by Greek Psi

These letters were used to a small extent on public inscriptions dating from his reign but their use was abandoned after his death. He may have been inspired to introduce these changes by a comment his mother Antonia made to him in his youth, to the effect of that Claudius would be as unlikely to become emperor as he would be able to change the alphabet.

However, later on, the letter Y was added, filling the role of his broken 'H'. His first innovation, however, would not catch on for over 1500 years, when U, V, and W became recognized as separate letters. (Up until the 17th century, U and V were represented by the same letter, printed V as capital, v initially, and u medially and finally, resulting in spellings such as "haue" and "vpon".)