The large sphere atop the Sasanian royal crown was called a korymbos. It was a globe-like, often jewel-adorned feature that contained or covered the ruler’s gathered topknot and rested above the crown.
The korymbos appears in surviving Sasanian royal imagery, especially on coins and monumental art. Its use is associated with the dynasty founded by Ardashir I, whose reign began in AD 224. The feature helped make the king’s silhouette immediately recognizable and contributed to the visual language of Sasanian sovereignty.
The term needs a small qualification: korymbos is a Greek scholarly label, not necessarily an indigenous Iranian name used by the Sasanians themselves. Its literal associations include a cluster or uppermost point, reflecting the rounded form seen in artistic representations.
A korymbos is not the same as a tiara, halo, or diadem. Those terms describe broader headgear or symbolic motifs, while korymbos identifies the distinctive spherical element on top of the Sasanian crown. Because depictions vary by ruler and period, historians sometimes debate construction details, but the identifying form is well established.