Back in mid-April there was an attack against the Sarafiya bridge in Baghdad which caused the bridge to collapse into the Tigris River.

The al-Sarafiya bridge was severely damaged in two places by this morning's pre-rush hour explosion, which collapsed the steel girders of one of the main crossing points in the northern half of Baghdad.

Iraqi authorities said that at least 26 people had been injured in the explosion but there were fears that the death toll could rise as police and dive teams searched the muddy waters of the Tigris for fallen vehicles and as many as 20 people who are thought to have been thrown off the bridge.

Then another bridge was attacked, unsuccessfully.

Meanwhile, in central Baghdad's Karradah district, a suicide bomber detonated his explosives on a bridge over the Tigris River. It is the second such attack in three days.

Then another Baghdad bridge was attacked.

Baghdad, Apr 14, (VOI) – Eight civilians were killed and 13 others wounded when a vehicle rigged with explosives blew up on a bridge in central Baghdad, an Iraqi police source said on Saturday. "A suicide bomber detonated his vehicle on the al-Jadiriya bridge on Saturday morning, killing eight people, wounding 13 others and damaging several nearby civilian vehicles," the source told the independent news agency Voices of Iraq (VOI). The source said security forces sealed off the area while ambulances rushed the wounded to nearby hospitals. Al-Jadiriya bridge, which links al-Karkh and al-Rasafa areas in Baghdad over the river Tigris, was built during the former regime's era and is considered one of the most important bridges in Iraq.

And then two more attacked on May 11th. COL Pat Lang discusses the situation, looking at the strategic, tactical, and political implications:

The campaign against the bridges continues in Baghdad. Two more bridges were attacked yesterday. These were across the Diyala River in southeast Baghdad. That makes five bridge attacks so far. Motive remains a question. My "working theory" is that the predominately Sunni insurgents are seeking to impede the "creeping" movement of Shia occupation of the city from east to west. A friend in Baghdad tells me that the "line" dividing the mainly Shia part of the city from the mainly Sunni is moving steadily westward to the disadvantage of the Sunnis. The goal would be a Shia dominated capital city. An alternative theory is that the insurgents are seeking to build impediments to the movement of coalition tactical reserves (QRF). Time will tell.

And then, on Wednesday:

Two bridges in Northern Iraq were destroyed in separate attacks, hours apart, including a bridge on the main road linking the city of Mosul to the Kurdish city of Arbil to the east, and a bridge linking Mosul to areas to the north and west.

Nineva province security forces announced that a bridge along the highway linking Mosul to Irbil, two cities some 50 miles apart, was destroyed Wednesday evening.

"Unknown gunmen this evening blew up Aski Bridge to the east of Mosul," Brigadier Said Ahmed, Ninewa police media spokesman, told Voices of Iraq (VOI).

The Aski bridge, located in the town of the same name, spanned a Tigris tributary known as the Zab al-Kabir.

Earlier, a police source said unknown gunmen detonated two car bombs on both sides of Badoush bridge in northern Iraq bringing down the bridge with no casualties, VOI writes.

All this could truly be part of a plan to continue the segregation of Sunni fighters from Shia portions of the county, or it could be opening rounds in a plan to isolate US units from support and reaction forces.

Losing all these bridges could make a tidy and safe withdrawal more difficult. As I speculated here, shooting our way out, but with a lack of bridges, could increase the pucker factor considerably.