From Halopedia, the Halo wiki
The barrier functions similarly to a large shield door, and bears a resemblance to the Deployable Cover equipment. It was first seen in use during the Harvest campaign, and several variants later used in 2552 during the Battle of Mombasa and on the Tsavo Highway to prevent UNSC forces from reaching Voi. The barriers seen in Mombasa were apparently a more advanced iteration of the technology, featuring a fully protected power source and not allowing enemy infantry to pass through. The power sources of the barriers are sometimes protected by additional sets of roadblocks.
In October 2558, during the Battle of Nuusra, Jul 'Mdama's Covenant deployed two of these barriers to block access through old ruins. Unlike the barriers encountered in Voi and on Harvest, infantry forces could not pass through these to reach the power source. Fireteam Osiris was able to take down the first one by heading through a side passage in a nearby where a small opening gave them a shot on the shield generator. In the second case, Osiris was able to break through a cracked wall below the shield's location and come up behind it to take out the shield generator.
On Genesis, the Covenant deployed several of these to protect one of the gravitational cores Osiris had to destroy to free Blue Team's Cryptum. Unlike the other barriers, these were vulnerable to weapons fire, particularly from a Mantis, taking down the shields and allowing Osiris to destroy the gravitational core and continue on with their mission.
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