It is Independence Day in Pakistan, an occasion traditionally celebrated with military parades and grandiose speeches, with poetry and prayers, and with a great deal of flourishing of the national flag.
But 67 years after this nation was carved out of the subcontinent at the end of British colonial rule, the capital is spending the day gripped by anxiety, and partially paralyzed by a government-enforced lockdown.
The citizens of Islamabad have long become used to checkpoints, razor wire and blast barriers, erected to thwart Islamist militants who occasionally target their city.
But in the past few days, Islamabad has looked like a fortress barricading itself against an onslaught from marauding invaders.
It's yet another reminder that, after a short history marred by coups and years of military dictatorship, Pakistan remains politically fragile, and also profoundly apprehensive about the future.
Two Separate Protest Marches
This time the perceived threat is not primarily from the Taliban or its allies, although the authorities are worried about suicide bombers infiltrating the city on a national day of great symbolic importance.
It is from a cavalcade of protesters one organized by a former sports star and the other by a populist cleric. The demonstrators are mustering in the eastern city of Lahore before rattling their way along the historic Grand Trunk Road en route to Pakistan's capital to demand the resignation of Prime Minister Nawaz Sharif.
One protest leader is cricketer-turned-politician Imran Khan, head of the second-largest opposition party in parliament.
Khan alleges that there was widespread rigging in the election that delivered Sharif's landslide victory last year, and argues that the government is therefore invalid. This week Sharif agreed to set up a judicial commission to investigate some of these claims.
This concession failed to mollify Khan, or to deter him from leading thousands of supporters on the Independence Day "march." The marchers will mostly travel in vehicles on the 185-mile route from Lahore to Islamabad.
The other man in the vanguard of the protests is Tahir ul-Qadri, a Pakistani cleric recently returned from Canada, where he's also a citizen.
Qadri portrays himself as a peaceful "revolutionary," a champion of the rights of the downtrodden. He promises his many thousands of acolytes that he will free Pakistan from chronic afflictions that include government corruption, mass poverty and tyrannical Islamist militants.
Qadri is also leading a throng of followers to Islamabad, a city that he brought to a grinding halt last year by leading a four-day sit-in with 50,000 devotees.
Although his march is separate from Khan's, these two hefty political pugilists seem to have come together in order to pile punches on Sharif.
A Tense Atmosphere
The atmosphere is tense and combustible, especially in the Qadri camp. In June, at least a dozen Qadri activists were killed after police opened fire on a crowd of his followers in Lahore. A few days ago, there were more clashes and several more fatalities.
Even so, the security preparations in Islamabad ahead of the marchers' arrival have been extraordinary. Over the past few days, giant steel shipping containers have been blocking highways and roads around the capital, either entirely sealing them off or reducing traffic to one lane, so that police can screen all vehicles entering the city.
Thousands of extra police, wielding riot shields and batons, have been drafted in from surrounding areas to man checkpoints and guard sensitive areas.
Army troops are posted outside the "Red Zone" the fortress neighborhood housing much of the international community. Mobile telephone services are partially cut. Many gas stations have been closed, causing an acute fuel shortage.
Hours after the marchers set off, it is still not clear what restrictions on their movement will be enforced when they reach the city.
The scale of this security operation has caused surprise here, as it looks like the action of a government that, after some 15 months in office, considers itself to be in a fight for survival. Although the government may be overreacting, this has fueled a general air of angst, causing the stock market and the rupee to dip, and food prices to rise.
The current jittery mood flows from another, deeper well a perennial suspicion among Pakistanis that the hugely powerful hand of the army and intelligence services is influencing events behind the scenes.
Relations between Sharif's government and the military are thought to be strained, not least because of treason charges leveled against ex-president and former army chief Gen. Pervez Musharraf. Speculation abounds that the military is quietly encouraging the government's opponents, in order to keep Sharif in check.
Sharif is dismissive of this idea.
"The military and civilian leadership is celebrating the independence day together," he said Thursday at one of many Independence Day ceremonies. "This is the revolution."
Yet it will take a lot more than a few reassuring words to dispel the deeply held view among some in Pakistan that, if there is serious unrest, the military could again take over and that, as Pakistan enters its 68th year, history will repeat itself.