A radiate head or bust is depicted wearing a radiate crown. The radiate crown is an attribute of the Sun god (Sol Invictus, Helios) and is conferring that association upon the wearer. Tiberius was the first emperor to depict the radiate crown on coin portraiture, but ONLY for posthumous portraiture of the deified Augustus. Nero was the Roman first to depict it on a living person (himself). As a bust attribute on some roman coins it served as a "double value" denominational marker: dupondius = double as, antoninianus = double denarius.
Many coins of Rhodes depict the sun god Helios with a radiate crown. These images inspired the radiate crown on the Statue of Liberty.Rhodos, Carian Islands, c. 229 - 205 B.C.
Today we associate the crown with royalty. The ancient Greeks associated the radiate crown with divinity and in the Hellenistic period royalty was often associated with divinity. With the beautiful and rare type below Ptolemy IV honored his deceased father with the symbols of divinity. He wears the aegis of Zeus, the radiate crown of Helios, and carries the trident of Neptune.
Ptolemaic Kingdom, Ptolemy IV, 221 - 204 B.C.
Gold oktodrachm, Svoronos 1117, SNG Cop 196, gVF, Alexandria mint, weight 27.788g, maximum diameter 26.9mm, die axis 0o, obverse radiate and diademed bust of the deified Ptolemy III; reverse BASILEWS PTOLEMAIOU, radiate cornucopia bound with royal diadem, DI below.
Tiberius was the first emperor to depict the radiate crown on coin portraiture, but ONLY for posthumous portraiture of the deified Augustus.
Augustus, 16 January 27 B.C. - 19 August 14 A.D., Commemorative Struck by Caligula
Orichalcum dupondius, SRCV I 1811, RIC I Gaius 56, BMCRE I 88, gVF, smoothed, weight 15.513g, maximum diameter 29.7mm, die axis 180o, Rome mint, 37 - 41 A.D.; obverse DIVVS AVGVSTVS S C, radiate head of Augustus left; reverse CONSENSV SENAT ET EQ ORDIN P Q R, Augustus laureate and togate, seated left on curule chair, branch in right, left at side.
Nero was the Roman first to depict it on a living person (himself). This was one act in a long list of egomaniacal behaviors that lead to rebellion against him and his suicide.
Nero, 13 October 54 - 9 June 68 A.D.
Orichalcum dupondius, BMCRE I 197, pl. 43.7 (same dies); RIC I 111, Maowall p. 56, 184 (7 spec. from 2 obv. and 1 rev. die); cf. Cohen 358 (10 Fr.), VF, Tiber patina, Lugdunum (Lyon) mint, weight 15.945g, maximum diameter 20.1mm, die axis 180o, 64 A.D.; obverse NERO CLAVD CAESAR AVG GER P M TR P IMP P, radiate head right; reverse anepigraphic, Macellum Magnum (great market), two-story, domed section, wings unequal height, steps with dolphin on each side, Neptune statue holding a long scepter inside.
The radiate crown came to mean a double unit denomination. The dupondius was worth two as. Caracalla introduced a double denarius (antoninianus) and used the radiate crown to clearly identify its value.
Caracalla, 28 January 198 - 8 April 217 A.D.
Silver antoninianus (double denarius), RSC III 608a, BMCRE V 78, RIC IV 311c var (seen from front), Choice VF, Rome mint, weight 5.421g, maximum diameter 23.7mm, die axis 0o, 213 - 217 A.D.; obverse ANTONINVS PIVS AVG GERM, radiate, draped and cuirassed bust right, from behind; reverse VENVS VICTRIX, Venus standing left, Victory in right, transverse scepter in left, leaning on shield set on helmet.
Another example where the radiate crown is used to indicate a double value is the radiate crown on the double sestertius below.
Trajan Decius, July 249 - First Half of June 251 A.D.
Orichalcum double sestertius, RIC IV 115a, Cohen 39, Choice VF, weight 34.518g, maximum diameter 36.3mm, die axis 180o, Rome mint, 249 - 251 A.D.; obverse IMP C M Q TRAIANVS DECIVS AVG, radiate and cuirassed bust right, drapery in left shoulder; reverse FELICITAS SAECVLI S C, Felicitas standing left, caduceus in right, cornucopia in left.