Classical Antiquity: Paleography
Section 4: Rustic Capitals
Several of the most famous copies of Vergil's works from the 5th and 6th centuries are in Rustic Capitals, and it is probably significant that only two of the surviving books in Rustic Capitals are copies of the works of Christian authors. The manuscript below is a famous manuscript of Vergil that has recently been digitized by the Vatican Library, the so-called "Vatican Vergil." It is roughly contemporary with the Vergil manuscript in Square Capitals that we looked at above.
Aspect and letterforms: Compared to Square Capitals, Rustic Capitals have a slender, laterally-compressed appearance. Letters are distinctly taller than they are wide. While Rustic Capitals also appear inscribed in stone in the Roman world, as a bookhand they do not give the impression of having been written in imitation of letters chiseled in stone. All the letters in Rustic Capitals are easily recognizable as our upper-case letters.
Like Square Capitals, Rustic Capitals had a long after-life as a display script in medieval manuscripts. The example of Rustic Capitals below is taken from a 9th-century manuscript in which the capitals serve as a display script. Note that a manuscript written all in Rustic Capitals from late antiquity would not have any separation between words of the sort you can see in this manuscript.
Rustic Capitals used as a display script in a 9th-century Carolingian manuscript
St. Gallen, Stiftsbibliothek, Cod. Sang. 152, p. 3. (www.e-codices.unifr.ch )