CAIRO; In a day full of memorable images, none on Saturday was more powerful than that of Egypt's first Islamist president, Mohamed Mursi, flanked by generals at a military parade where he was formally handed authority to govern the nation.

For six decades, Mursi's seat had been filled by presidents drawn from the ranks of the military. And for half that time, it was occupied by one man, Hosni Mubarak, a former air force chief who hounded and jailed members of Mursi's Muslim Brotherhood.

Now the tables are turned, even if the presidential office Mursi holds has been shorn by the generals of many of powers Mubarak and his predecessors enjoyed.

"We have kept the promise that we made before God and the people. Now we have an elected president who takes over the keys for ruling Egypt through a direct and free vote," said Field Marshal Hussein Tantawi, addressing his guest as "Mr President".

Before that, state television showed Tantawi, Egypt's top general and Mubarak's loyal defence minister for 20 years, welcoming Mursi as he stepped out of a black sedan at the desert base with a hurried salute before shaking his hand.

It was not just the military ceremony that oozed symbolism.

Mursi addressed the nation from the same stage in Cairo where U.S. President Barack Obama had in 2009 appealed to Arab autocrats to open up. Egypt's new leader was sworn in at a court next to the hospital where imprisoned Mubarak is being treated.

But it was the scene at Heikstep military base that captured Egypt's dramatic transformation most clearly with images unthinkable a year-and-a-half ago before Arab uprisings challenged autocrats who had ruled the region for generations.

"A picture for history: a civilian president in the middle of the military," wrote Dima Khatib on Twitter, one of the social networking sites that was used to galvanise the masses against Mubarak, toppling him on February 11, 2011 after 18 days.

MILITARY HONOURS

Mursi was given a 21-gun salute, helicopters flew past to honour him and troops stood to attention in serried ranks.

Those acts of respect did not however signal generals were retiring to barracks to leave civilians completely in charge.

In a decree issued as this month's run-off presidential elected ended, the military council declared the next president would not command the armed forces and could not declare war alone. It also said the army would have legislative powers until a new parliament is elected to replace one dissolved this month.

But the ceremony showed the military, one of the few state institutions to survive the post-Mubarak turmoil intact, now has to accept that its erstwhile adversary, the Brotherhood, has a popular mandate to help determine Egypt's future.

"The Egyptian people and the ... world are witnessing a unique model, not seen before, of how power is transferred from the Egyptian military forces by the will of the people to an elected, civilian power," Mursi said, hailing the military, but also sending a clear message to the men in uniform.

Tantawi shook Mursi's hand firmly as he handed him a plaque bearing a military shield. Mursi then joined a gaggle of senior officers who lined up around him for a group photo.

Mursi had earlier delivered a speech at Cairo University on the same podium from which Obama addressed the Arab and Muslim world early in his presidency, reaching out to a region angry at U.S.-led wars in Afghanistan and Iraq over the previous decade.

"America respects the right of all peaceful and law-abiding voices to be heard around the world, even if we disagree with them," Obama told the audience at the time.

Yet when protests against Mubarak erupted on January 25, 2011, many Egyptians were dismayed by how long it took Obama to ditch the president who had become a linchpin ally in the region and guardian of the U.S.-sponsored peace treaty with Israel.

CHANTS AND COUNTER-CHANTS

Washington, long wary of political Islam, took several more months before opening formal channels to the Brotherhood.

The Brotherhood was itself slow to send supporters onto Cairo's streets in the uprising, anxious to avoid a crushing response from Mubarak's police after being bruised by earlier crackdowns that the group had struggled to survive.

But the Brotherhood has emerged as the biggest beneficiary of a revolt ignited by young, secular liberals.

In his speech Mursi pledged to serve the whole nation and secure rights for the families of those killed in the uprising.

"Free revolutionaries, we will complete our journey," some in the audience chanted as he wrapped up his address.

Tantawi joined guests in the university hall, applauding when Mursi lauded the armed forces, seated alongside Christian priests, Muslim preachers, veiled women and suited men.

"Down with military rule," some had briefly chanted when Tantawi entered, before an official guided those present towards a more respectful: "The army and people, one hand."

Mursi had pulled up in a cavalcade, but unlike in Mubarak's day, the whole capital was not brought to a grinding halt by police blocking every road to clear the president's route.

Cars passed freely along the Nile-side road in front of the Supreme Constitutional Court even as Mursi swore his oath.

The oath is usually held before parliament, but the location was forced on the Brotherhood man after the same constitutional court, stuffed with judges appointed in Mubarak's era, dissolved the Islamist-led parliament, a ruling the army swiftly enforced.

Yet the venue carried its own mordant twist, standing next to Maadi military hospital where Mubarak, jailed for life for failing to stop the killing of protesters, is being treated. He was moved there from a prison medical centre last week.

In that same Maadi hospital set in lush gardens, Mubarak's predecessor Anwar Sadat was pronounced dead after Islamists gunned him down in 1981. The exiled shah of Iran died there after the 1979 Islamic revolution. AGENCIES