Even the most ardent in calling for his prosecution doubted until hours before the trial began that the 83-year-old former president would appear in a cage fashioned of bars and wire mesh, a reflection of the suspicion and unease that reigns in a country whose revolution remains unresolved. As a helicopter ferried him to the courtroom, housed in a police academy that once bore his name, cheers went up from a crowd gathered outside.

“The criminal is coming!” shouted Maged Wahba, a 40-year-old lawyer.

The sheer symbolism of the day made it one of the most visceral episodes in modern Arab history. In a region whose destiny was so long determined by rulers who deemed their people unfit to rule, one of those rulers was being tried by his public. On this day, the aura of power — uncontested and distant — was made mundane, and Mr. Mubarak, dressed in white and bearing a look some read as disdain, was humbled.

“The first defendant, Mohammed Hosni al-Sayyid Mubarak,” the judge, Ahmed Rifaat, said, speaking to the cage holding Mr. Mubarak and his codefendants — his two sons, Gamal and Alaa, former Interior Minister Habib el-Adly and six other senior police officers.

“Sir, I am present,” Mr. Mubarak replied into a microphone, from his bed.

“You heard the charges that the prosecutor made against you,” the judge said from his podium in the wood-paneled courtroom. “What do you say?”

“I deny all these accusations completely,” he replied, wearily waving his hand. Then he handed the microphone to his son, Gamal.

With those words, the might of those epic protests in Tahrir Square were incarnated in one man, Mr. Mubarak, who last appeared in public on February 10, when he uttered a phrase that suggested the heedlessness of absolute authority. “It's not about me,” he said then, to the disbelief of hundreds of thousands demonstrating in his capital. On this day, television captured him picking his nose. The two lines were the only words he uttered to the judge. Hard of hearing, his son had to repeat the judge's question to him.

“God brings glory to whoever he wants and humiliates whoever he wants,” several onlookers said, quoting a Koranic verse, as Mr. Mubarak appeared on the screen.

The trial began precisely at its start time, 10 am in Cairo. While the other defendants took a seat, Mr. Mubarak's sons remained standing, the youngest, Gamal, seeming to block the view of his father from the cameras in the courtroom. Mr. Mubarak appeared tired but alert, occasionally speaking with his sons, who both held Korans.

As Mr. Mubarak denied the charges in the proceedings, broadcast on a huge television outside the police academy, his opponents gathered there roared in disapproval.

“Then who did it?” some asked.

The scene was tumultuous there on a sun-drenched parking lot, with a few dozen of Mr. Mubarak's supporters sharing space with his opponents. At times, they scuffled; in intermittent clashes, the two sides threw rocks at each other. As Mr. Mubarak arrived at the courtroom, some of his supporters cried, waving pictures that read, “The insult to Mubarak is an insult to all honorable Egyptians.” Others shouted adulation at the screen.

“We love you, Mr. President!,” some chanted.

Those sentiments were overwhelmed by the denunciations of his critics, in a trial that, for a moment, seemed to represent all the frustrations and degradations of a state that treated its people as rabble. Someone was finally being held to account, many said.

“Today is a triumph over 30 years of tragedy,” said Fathi Farouk, a 50-year-old pharmacist who brought his family to watch the trial outside the academy. “We suffered for 30 years and today is our a victory. It’s a victory for the Egyptian people.”

The trial has transfixed a turbulent Arab world, where uprisings have shaken the rule of autocrats and authoritarian rule in Libya, Syria, Yemen and Bahrain. Some Arab officials have said the very spectacle of the trial — a president and members of his family, along with his retinue of officials facing charges — would make those leaders all the more reluctant to step down. On the very day Mr. Mubarak's trial began, President Bashar al-Assad of Syria escalated his own crackdown on a city at the heart of the uprising against him.

But many gathered here said Arabs should take the opposite lesson from the proceedings. “All of the Arab world has to know that any leader who makes his people suffer will face this fate,” Mr. Farouk said. “From today, history will never be the same.”

Indeed, the country was awash in cries for justice, calls for vengeance and, not uncommon, expressions of regret for the fate of an old man who never seemed quite as loathsome as some of his contemporaries. There was fascination at the spectacle itself. “I am dreaming,” said Hossam Mohammed, as he watched the trial. “Somebody pinch me.” Others saw a reckoning with the past.

“When you enter the cage yourself, then you're freed after the revolution, then you see the one who imprisoned you and his kids in the cage, it's a magnificent scene,” said Yehia Khalaf, a former Islamic militant jailed for 18 years under Mr. Mubarak.

Mr. Mubarak's health had remained an issue before the proceedings. Since April, when he was accused of the charges, he has resided in a hospital in the Sinai resort of Sharm el-Sheikh, a favorite retreat during his time in power. There were reports that he had stopped eating, entered a coma and become depressed, but Egypt's health minister said the former president was well enough to make the trip to the police academy in the capital.

Only the 600 people with permits were allowed inside the courtroom, along with civil rights lawyers and a small number of the families of protesters killed in the uprising.

As late as Wednesday morning, there was speculation that Mr. Mubarak would not appear, given the remarkable humiliation that the trial represented. The military council of 19 generals that has led Egypt since the revolution seemed loathe to put one of their own — their former commander, no less — in a courtroom; in fact, many speculated that the council hoped he might pass away before the date arrived. But frustration has grown lately at the military council, whose decisions are opaque at a time that Egypt feels unmoored and especially anxious, and some people believed that the threat of even more protests had forced the military's hand.

“This trial is going to end a lot of our problems and restore the trust between the revolutionaries and the military council,” said Ahmed Gamal, a 65-year-old retiree, who planned to watch the trial from beginning to end. “This is the most important thing.”

Much of the trial's opening was occupied by procedural matters, but even that came as a surprise, as many expected a quick adjournment. Mr. Mubarak and his sons were not even read their charges until the trial's second hour, after a brief recess. Wednesday's sessions lasted about four hours and was then adjourned until August 15.

The judge promised speedy proceedings, though no one seemed to know whether that meant weeks, months or longer. Egyptian officials said Mr. Mubarak would remain in the capital for the duration of the trial, staying at a hospital on Cairo's outskirts.

Mr. Mubarak, the former interior minister and the six officers are charged in connection with killing protesters. The charges can carry the death penalty. Mr. Mubarak and his sons also face charges of corruption, though the allegations — that they received five villas to help a businessman buy state land at a cheaper price — paled before some of the more epic cases of corruption in a country riddled with patronage and misrule.

The spectacle of the trial, though, seemed to matter more than the charges.

As a headline in a popular Egyptian newspaper read: “The Day of Judgment.”

Heba Afify contributed reporting.