In Politics and Script. . . . Barker ed. (1972) Stanley Morison considered a fragment of a papyrus roll of the Epitome of Livy preserved in the British Museum (P. 1532) to be the earliest stage of half-uncial calligraphy. The papyrus was found at Oxyhynchus, Egypt in 1903 "along with cursive documents of the second, third, and fourth centures. In the first half of the fourth century the back of the roll was used to write the Epistle to the Hebrews in Greek uncial (P. Oxy. No. 657), which furnishes a terminus ad quem for the Latin script. Acquired by the British Museum in 1906" (Lowe, Codices Latini Antiquiores II, no. 208).
Grenfell & Hunt, Oxyrhynchus Papyri IV (1904) 90 describe the writing on this papyrus as "a medium-sized upright uncial, with some admixture of minuscule forms (b, d), and belongs to the same class as the Vergil fragment (P. Oxy. I, Plate viii) and the Bodleian Chronicles of Eusebius (Palaegraphical Soc. II. Plate 130), but is an earlier example of the mixed style than has hitherto been known. . . ."
Lowe, characterized the script as "calligraphic but provincial," partly in uncial and "b, d, r, m" as "distinctly half-uncial."
Morison, Politics and Script, 78-79, pl. 57.