Thuluth is the great display script of Islamic calligraphy, tall, sweeping and dramatically curved, its name meaning a third, generally explained by classical calligraphers as referring to the proportion of each letter's curve to its straight strokes within the script's codified geometric system, the same proportional discipline developed by Ibn Muqla and his successors that also governs naskh. Where naskh was refined for legibility at ordinary reading scale, thuluth was developed and prized precisely for its impact at large scale and from a distance, its elongated verticals, deep curves and interlocking letterforms making it the preferred script wherever sacred text needed to command a large public space rather than be read closely, mosque friezes running the full length of an interior wall, the great domes of major mosques, and the monumental bands of inscription encircling significant Islamic buildings across the medieval and early modern Islamic world.
The hilya, a formal calligraphic composition describing the Prophet Muhammad's physical appearance and character based on hadith reports, is traditionally rendered in thuluth or in a closely related script, treated as a devotional object in its own right, displayed in homes and mosques as an act of reverence toward the Prophet expressed through the discipline of the written word rather than through any pictorial image, which classical Islamic practice generally avoids for the Prophet's person.