Herodian, Histories (5.6)
“His outfit was something between a Phoenician priest’s and the luxury of the Medes. He hated both Roman and Greek dress because they were made of wool, which he said was cheap. He only allowed himself to be adorned with silk, and only went out accompanied by flutes and cymbals as if celebrating the rites of his favorite god.
Julia Maesa was vexed when she saw all this, and with some considerable effort tried to persuaded him to put on Roman garb as he was on his way to the city and the senate house, lest he seem to everyone outfitted in something foreign or barbaric and immediately irritate all those who saw him, especially since they were unaccustomed to see things like that, considering that such beautiful finery was more fitting for women than for men. Elagabalus thought little of the advice of the old woman, and was not persuaded by anyone else, because he never allowed anyone to approach him except for those who shared his habits or encouraged his vices.
Hoping, however, to make the Roman people and senate more accustomed to the sight of his dress despite the fact that he was not yet in the city and to see how they would react to the appearance of his outfit, he had a large portrait of himself painted in which he appeared alone strutting forth and performing sacred rites, and set beside it a picture of the god of his land, to whom he was depicted sacrificing. He sent this to Rome, and ordered it to be placed squarely in the middle of the senate house above the statue of Victory, to which visitors in the senate house go to burn incense and pour libations.”

ἦν τε αὐτῷ τὸ σχῆμα μεταξὺ Φοινίσσης ἱερᾶς στολῆς καὶ χλιδῆς Μηδικῆς. ῾Ρωμαϊκὴν δὲ ἢ ῾Ελληνικὴν πᾶσαν ἐσθῆτα ἐμυσάττετο, ἐρίου φάσκων εἰργάσθαι, πράγματος εὐτελοῦς· τοῖς δὲ Σηρῶν ὑφάσμασι μόνοις ἠρέσκετο. προῄει τε ὑπὸ αὐλοῖς καὶ τυμπάνοις, τῷ θεῷ δῆθεν ὀργιάζων.
ἡ δὲ Μαῖσα ταῦτα ὁρῶσα πάνυ ἤσχαλλε, πείθειν τε λιπαροῦσα ἐπειρᾶτο μεταμφιέσασθαι τὴν ῾Ρωμαίων στολὴν μέλλοντά [τε] ἐς τὴν πόλιν ἀφίξεσθαι καὶ ἐς τὴν σύγκλητον εἰσελεύσεσθαι, μὴ ἀλλοδαπὸν ἢ παντάπασι βάρβαρον τὸ σχῆμα ὀφθὲν εὐθὺς λυπήσῃ τοὺς ἰδόντας, ἀήθεις τε ὄντας καὶ οἰομένους τὰ τοιαῦτα καλλωπίσματα οὐκ ἀνδράσιν ἀλλὰ θηλείαις πρέπειν. ὃ δὲ καταφρονήσας τῶν ὑπὸ τῆς πρεσβύτιδος λεχθέντων, μηδ’ ἄλλῳ τινὶ πεισθείς (οὐδὲ γὰρ προσίετο εἰ μὴ τοὺς ὁμοιοτρόπους τε καὶ κόλακας αὑτοῦ τῶν ἁμαρτημάτων), βουλόμενος ἐν ἔθει γενέσθαι τῆς τοῦ σχήματος ὄψεως τήν τε σύγκλητον καὶ τὸν δῆμον ῾Ρωμαίων, ἀπόντος τε αὑτοῦ πεῖραν δοθῆναι πῶς φέρουσι τὴν ὄψιν τοῦ σχήματος, εἰκόνα μεγίστην γράψας παντὸς ἑαυτοῦ, οἷος προϊών τε καὶ ἱερουργῶν ἐφαίνετο, παραστήσας τε ἐν τῇ γραφῇ τὸν τύπον τοῦ ἐπιχωρίου θεοῦ, ᾧ δὴ καλλιερῶν ἐγέγραπτο, πέμψας τε ἐς τὴν ῾Ρώμην, ἐκέλευσεν ἐν τῷ μεσαιτάτῳ τῆς συγκλήτου τόπῳ ὑψηλοτάτῳ τε τὴν εἰκόνα ἀνατεθῆναι ὑπὲρ κεφαλῆς τοῦ ἀγάλματος τῆς νίκης, ᾧ συνιόντες ἐς τὸ βουλευτήριον λιβανωτόν τε θυμιῶσιν ἕκαστος καὶ οἴνου σπένδουσι.