Thuluth is an Arabic script variety of Islamic calligraphy. The straight angular forms of Kufic were replaced in the new script by curved and oblique lines. In Thuluth, one-third of each letter slopes, from which the name comes. An alternative theory to the meaning is that the smallest width of the letter is one third of its widest part. It is an elegant, cursive script, used in medieval times on mosque decorations. Various calligraphic styles evolved from Thuluth through slight changes of form.