Comazon and other allies of Julia Maesa and Elagabalus are given powerful and lucrative positions in the autumn of 219 when the new emperor’s entourage reaches Rome, much to the outrage of many senators who do not consider them to be respectable.

After Comazon's tenure as Praetorian prefect, he will serve as the city prefect of Rome three times, and as consul twice.

Elagabalus soon devalues the Roman currency, decreasing the silver purity of the denarius from 58% to 46.5%—the actual silver weight dropping from 1.82 grams to 1.41 grams.

He also demonetized the antoninianus during this period in Rome.

Elagabalus tries to have his presumed lover, the charioteer Hierocles, declared Caesar, while another alleged lover, the athlete Aurelius Zoticus, is appointed to the non-administrative but influential position of Cubicularius.

His offer of amnesty for the Roman leadership is largely honored, though the jurist Ulpian is exiled.

The relationships between Julia Maesa, Julia Soaemias, and Elagabalus are strong, at first.

His mother and grandmother become the first women to be allowed into the Senate, and both received senatorial titles: Soaemias the established title of Clarissima and Maesa the more unorthodox Mater Castrorum et Senatus.

While Julia Maesa tries to position herself as the power behind the throne and subsequently the most powerful woman in the world, Elagabalus will prove to be highly independent, set in his ways, and impossible to control.

Sun worship has increased throughout the Empire since the reign of Septimius Severus.

Elagabalus, in his dual role as Roman Emperor and hereditary priest of the god El-Gabal at his hometown, Emesa, sees this as an opportunity to install El-Gabal as the chief deity of the Roman Pantheon.

The god is renamed Deus Sol Invictus, meaning God the Undefeated Sun, and placed over Jupiter.

As a sign of the union with the Roman religion, Elagabalus gives either Astarte, Minerva, Urania, or some combination of the three, to El-Gabal as a wife.

He provokes further outrage when he takes as his second wife the Vestal Virgin Aquilia Severa, claiming the marriage will produce "god-like children".

This is a flagrant breach of Roman law and tradition, which holds that any Vestal found to have engaged in sexual intercourse before her thirty-year vow of celibacy has been fulfilled is to be buried alive.

A lavish temple called the Elagabalium is built on the east face of the Palatine Hill to house El-Gabal, who is represented by a black conical meteorite from Emesa.

Herodian wrote "this stone is worshipped as though it were sent from heaven; on it there are some small projecting pieces and markings that are pointed out, which the people would like to believe are a rough picture of the sun, because this is how they see them".

(Herodian, Roman History V.3) In order to become the high priest of his new religion, Elagabalus has himself circumcised.

(Cassius Dio, Roman History LXXX.11) He forces senators to watch while he dances around the altar of Deus Sol Invictus to the sound of drums and cymbals, and each summer solstice he holds a festival dedicated to the god, which becomes popular with the masses because of the free food widely distributed there.

During this festival, Elagabalus places the Emesa stone on a chariot adorned with gold and jewels, which he parades through the city.

The most sacred relics from the Roman religion are transferred from their respective shrines to the Elagabalium, including the Great Mother, the fire of Vesta, the Shields of the Salii and the Palladium, so that no other god except El-Gabal will be worshipped.

Elagabalus' eccentricities, particularly his relationship with Hierocles, have by 221 increasingly infuriated the soldiers of the Praetorian Guard, a significant portion of whom are Illyrians, having distinguished themselves as warriors in the Roman legions.

When Elagabalus’s grandmother, Julia Maesa, perceives that popular support for the emperor is quickly wavering, she decides that he and his mother, who had encouraged his religious practices, have to be replaced.

As alternatives, she turns to her other daughter Julia Avita Mamaea and her son, the thirteen-year-old Severus Alexander.

Persuading Elagabalus to appoint his cousin as his heir, Alexander is bestowed with the title of Caesar and shares the consulship with the emperor this year.

However, Elagabalus reconsiders this arrangement when he begins to suspect that the Praetorian Guard favors his cousin over himself.

Elagabalus' sexual orientation and gender identity are the source of much controversy and debate.

All told, Elagabalus will marry and divorce five women, three of whom are known.

His first wife was Julia Cornelia Paula; the second is the Vestal Virgin Julia Aquilia Severa, but within a year, he abandons her and marries Annia Aurelia Faustina, a descendant of Marcus Aurelius.

It is her beauty and her high prominent imperial ancestry that have attracted Elagabalus to her.

In order to marry her, he orders the execution of her husband, Pomponius Bassus.

After the death of the latter, Elagabalus forbids her to mourn Bassus.

In July 221, Elagabalus takes Faustina as his third wife.

Roman society is more accepting of his marriage to her than of his second marriage to the Vestal Virgin Julia Aquilia Severa.

Through her marriage to Elagabalus, she becomes Empress of Rome.

When she marries Elagabalus, it seems for a time that the Nerva–Antonine dynasty rule has returned to Rome.

He gives her the title of Annia Faustina Augusta and adds the Latin name Julia to her name.

Numismatic and other evidence that have survived of her date from her second, brief marriage, to Elagabalus.

Elagabalus has hoped she will bear him an heir, so that his maternal cousin will not inherit the throne; however, she bears him no children and, towards the end of 221, Elagabalus divorces her; it is not known why.

There are no surviving sources stating how Annia Aurelia Faustina ruled when she was a Roman Empress.

Elagabalus returns to Julia Aquilia Severa, claiming that the original divorce was invalid, and remarries her, as his fourth wife.

Although Elagabalus returns to Severa by the end of the year, according to Cassius Dio, his most stable relationship seems to have been with his chariot driver, a blond slave from Caria named Hierocles, whom he refers to as his husband.

The Augustan History claims that he also married a man named Zoticus, an athlete from Smyrna, in a public ceremony at Rome.

Cassius Dio reported Elagabalus would paint his eyes, epilate his hair and wear wigs before prostituting himself in taverns and brothels, (Cassius Dio, Roman History LXXX.14) and even the imperial palace: Finally, he set aside a room in the palace and there committed his indecencies, always standing nude at the door of the room, as the harlots do, and shaking the curtain which hung from gold rings, while in a soft and melting voice he solicited the passers-by. (Cassius Dio, Roman History LXXX.13)

Herodian commented that Elagabalus pampered his natural good looks by wearing too much make-up.

He was described as having been "delighted to be called the mistress, the wife, the Queen of Hierocles" and was said to have offered vast sums of money to the physician who could equip him with female genitalia. (Cassius Dio, Roman History LXXX.16)

Subsequently, Elagabalus has often been characterized by modern writers as transgender, most likely transsexual.

Elagabalus, to see how the Praetorians would react following the failure of various attempts at Alexander's life, strips his cousin of his titles, revokes his consulship, and circulates the news that Alexander is near death.

A riot ensues, and the guard demands to see Elagabalus and Alexander in the Praetorian camp.

The emperor complies and on March 11, 222, he presents his cousin, along with his mother Julia Soaemias.

Upon arrival the soldiers start cheering Alexander, while ignoring Elagabalus, who orders the summary arrest and execution of anyone who had taken part in this revolt.

In response, the Praetorians attack Elagabalus and his mother:

So he made an attempt to flee, and would have got away somewhere by being placed in a chest, had he not been discovered and slain, at the age of 18. His mother, who embraced him and clung tightly to him, perished with him; their heads were cut off and their bodies, after being stripped naked, were first dragged all over the city, and then the mother's body was cast aside somewhere or other, while his was thrown into the river. (Cassius Dio, Roman History LXXX.20)

Following his demise, many associates of Elagabalus are killed or deposed, including Hierocles and Comazon.

His religious edicts are reversed and El-Gabal is returned to Emesa.

Women are barred from ever attending meetings of the Senate, and damnatio memoriae—erasing a person from all public records—is decreed upon him.

The source of many of these stories of Elagabalus's debauchery is the Augustan History (Historia Augusta), which scholarly consensus now feels to be unreliable in its details.

The Historia Augusta was most likely written near the end of the fourth century during the reign of emperor Theodosius I, drawing as much upon the invention of its author as actual historical sources.

The life of Elagabalus as described in the Augustan History is believed to be largely a work of historical fiction.

Only the sections 13 to 17, relating to the fall of Elagabalus, are considered to hold any historical value.

Sources more credible than the Augustan History include the contemporary historians Cassius Dio and Herodian.

Cassius Dio's account of his reign is generally considered more reliable than the Augustan History, although it should be noted that Dio, although he was a contemporary of Elagabalus, spent the larger part of this period outside of Rome and had to rely on secondhand accounts when composing his Roman History.

Furthermore, the political climate in the aftermath of Elagabalus' reign, as well as his own position within the government of Alexander, likely imposed restrictions on the extent to which his writing on this period is truthful.

Herodian is considered the most important source on the religious reforms which took place during the reign of Elagabalus, which have been confirmed by modern numismatical and archaeological evidence.

While Herodian is deemed not as reliable as Cassius Dio, his lack of literary and scholarly pretensions make him less biased than senatorial historians.