Celtic calligraphy includes five main scripts: the Uncial style, which is the most common and popular, the half-uncial, the square script called like this due to the aspect of capitals, the cursive capitals and the runic script or ogham.
All these writing styles were adopted and stylized by Celtic monks, somewhere around 700 or 800 BC, and in the beginning they were used mainly to illustrate manuscripts and papers documenting historical events.
The Uncial script uses entirely capital letters or majuscules. Although it appeared between 3rd and 8th centuries in ancient Roman Republic, and was often used by Greek scribes as well, it became more popular after being brought to Irish or Celtic countries.
Due to the aspect of the capital letters, it is thought that this Celtic calligraphy style was developed from a late Old Roman style, probably a cursive one. Letters in this style are rather round and made of single strokes, but in the beginning they were often written separately.
Once the vellum and parchment writing surfaces were brought to these countries, the Uncial script started to be simplified and reshaped, as it was easier for the scribes to draw all the letters connected. And this is how the cursive appearance of this script became widely used.
As time passed and the style evolved, it started using flowers and other decorative motifs, as well as variable width strokes. While some letters were done using curved strokes, others were rather narrow or even drawn haphazardly. Although this technique made the script easier and faster to represent, it also altered its original appearance. Simplified, more compact and smaller Celtic calligraphy styles started to develop.
Another Irish script is the half-uncial, originated in the Old Roman script and brought to Ireland during the 5th century but it only became popular during the mid 18th century. Firstly used for religious texts and legal writings, this style was pretty similar to the regular Uncial script, although it wasn't derived from it.
Characterized by round letters with vertical stems or flat tops or curved shafts, the half-uncial wasn't as popular as the previously mentioned one. And although two different styles derived from this script, none of them was as widely spread as the Uncial lettering.
As for the Ogham alphabet, this appeared between the 4th and 6th centuries AD and it was firstly used in Christian writings. This Celtic calligraphy script is considered the first Irish one, as it wasn't derived from any Latin or Greek style.
Often called 'the tree alphabet' due to the medieval Irish tradition of writing names on trees, the Ogham style was also used for decorating stone monuments and other personalized objects. In fact, the first Runic inscriptions were represented almost exclusively of personal names, but it is presumed other short messages carved in metal or wood were also using this script.
Letters in this Celtic calligraphy styles were constructed using combinations of straight lines, placed adjacent or sometimes crossing an imaginary midline. Each letter contained up to five angled or vertical strokes and dots were often used for marking some vowels or spacing the words.