As the sun sets in the west, the Arabian sands swallow up a convoy of armed might that snakes incessantly north toward the confluence of the Tigris and Euphrates Rivers - and the prize target of Baghdad.
When the US advance is complete and the siege of the city begins - something that could be days or weeks away - the campaign will have entered its most crucial and uncertain stage.
"The siege of Baghdad is what the fight for Iraq has always been about," says Paul Beaver, a military analyst for the British Broadcasting Corp. "But US commanders still face the same problem ... as we see smaller sieges developing across the country. The allied forces have to fight on Saddam Hussein's terms, since he still controls these key population centers."
US officials say that the timing for a siege and attack on Baghdad are under intense discussion, with senior Pentagon officials arguing against a rush into heavy fighting.
Some young marines have said in recent days that they do not expect any siege to begin for at least two weeks because of overstretched supply lines and Iraqi resistance.
The Associated Press reported yesterday that military officials told troops with one frontline unit the pause could last 35 to 40 days, longer than a pause of up to six days they were warned of Saturday. At a briefing yesterday at Camp Doha in Qatar, Gen. Tommy Franks denied there is any pause on the battlefield.
Secretary of Defense Donald Rumsfeld has hinted the US military prefers the idea of a siege of Baghdad - a blockade that cuts off the city from outside sources - to the kind of violent street fighting that could make invading US forces look more like conquerors than liberators.
Anticipating the assault on the capital, Saddam Hussein has embedded his elite forces with the civilian population, say Iraqi officials and Western military sources. He appears anxious to draw Western armies into a trap, they add.
"The Iraqi leadership is playing a game now where it actually concedes defeat somewhere way down the road," says Michael Corgan, a military historian based in Boston. "The regime is hoping that this road is too long and unbearable for the United States. It expects that the siege of Baghdad will end when the US is itself so isolated by negative international public opinion that it can't go on."
That is because, regardless of their length, military sieges can take a heavy toll on general populations first, and fighters second.
"In siege warfare, you invariably try to put pressure on those inside to use up their supplies and resources," says Mr. Corgan. "Surely, great hardships will fall on the Iraqi people. Since Saddam Hussein's elite Republican Guard has no history of showing concern for their fellow citizens, the civilian plight is likely to grow increasingly worse under any kind of siege."
The ensuing publicity could be tremendously damaging to US interests, he adds.
The US military is considering a more moderate approach to any siege of Baghdad. In recent years, military planners have evaluated a type of siege, or loose cordon, that emphasizes starving out leaders, not civilian populations. It encourages civilians to leave their city and provides aid once they do.
Mr. Beaver says that the problems faced by US and British forces in other major populations centers across Iraq, from the ongoing British cordoning off of Basra in the south to Iraqi attacks on US positions near Najaf in the center, suggest that "the US and British military hasn't yet found a way engage against these population centers."
The US juggernaut that looked like a blitzkrieg when it began to roll 10 days ago has now slowed to a crawl as US and British commanders consider the growing needs of their own troops and Iraqi civilians. Infantry has spread out in the desert in tight formation and large artillery guns point both north towards Baghdad and off to the sides.
For each fighter at the "spearhead" of the US and British advance, an estimated nine soldiers must work diligently behind the lines to keep supplies flowing to the front.
The Pentagon has announced that 120,000 more US troops are en route to the region to take up the slack. With some 250,000 already in place, the number of committed troops is approaching 400,000-plus.
Supplies that forces bring in - ammunition, food, humanitarian assistance - are likely to remain under constant attack. "We are forced to keep up a vigilant patrol all along the convoys that come and go, almost as though this was another frontline," says Lt. Col. Bob Abbott, chief of military police patrols on the main highway running north to Baghdad from Kuwait.
These are just a few of the new "force protection" requirements brought on by intense guerrilla activity - including suicide-bombing strikes - in the Iraqi desert.
Coalition tanks, personnel carriers, and Mash units have now arrayed themselves 50 to 100 miles south of the capital, but are still struggling to encircle the capital.
Tightening the noose, say military experts, will leave the Iraqi regime on its own to face the world's most powerful military machine. A siege, once in place, would also prevent individual fighters and paramilitaries from across the Arab world from slipping into Baghdad to defend their Iraqi brethren.
"The pressure in besieged Baghdad could become so great that it could be a bloodbath, not just our bloodbath," says Corgan. "Internal strife, even if it brought heavy casualties, could offer US officials a useful denial that they were responsible. It could also bring about the fall of the regime."