They appear in a book from 1500, somewhat hidden in a woodcut. Saint Catherine of Siena (1347-1380) is depicted holding an open book, in which you can find these four words. This is the first edition of her letters, printed in Venice by the famous printer Aldus Manutius, a copy of which is also available in the BPH.

Italics, which are very familiar to today's readers, did not exist as printed letters before 1500. They were designed in Italy by the typecutter Francesco Griffo as an imitation of the humanistic handwriting commonly used there. In Germany, where the art of printing was invented around 1450, the handwriting looked very different, and the first printed letters were based on the Gothic script commonly used there.  

This cursive style of writing originated in Italy in the 15th century and combined two advantages: it was possible to write faster because the letters could be formed with a much smoother movement of the pen than the angular Gothic script, and the letters imitated the characteristics of the ancient Roman script found in inscriptions, which people had just begun to admire at that time.

In these few italic words in St. Catherine’s Epistole we do not yet see any capital letters, something you would certainly expect in the name of Jesus. This shows that the letters were probably still in the development phase. Letters were cast individually in molds. It seems that the molds for the lowercase letters were ready, but those for the capital letters were not. In 1501, an entire book was printed in italics for the first time, including capital letters (an edition of Virgil, also by Aldus Manutius).

This font allowed more text to be printed on a page, saving paper. As a result, long texts could still fit into a small-format book. This marked the birth of the first pocket books: yet another innovation devised by the Venetian printer Aldus! Nowadays, we hardly ever use italics as the main typeface for the body text, but only to make a section of text stand out.