The Shield Wall was the core interceptor and protection mechanism in Haven City up until Jak II. It was originally built by Mar and ran on the eco grid. The shield served its purpose for centuries before it was sabotaged by the Metal Head leader, Metal Kor. The city was breached by Kor's treachery, but Kor was defeated by Jak before it could be destroyed. Due to the subsequent War for Haven City taking place inside the city, the Shield Wall was not used, especially since the power station operating it was in KG Death Bot territory.
Most pertaining to the Shield Wall remains unknown. There is a large, concrete wall standing very high around the perimeter of the entire city, with airlocked exit points at the entrances to Haven Forest, pumping station, and Dead Town (however the latter and former cases were rendered inaccessible during Jak 3). It is presumed that the Shield Wall merely disabled opposing factions, as its physicality was neither observed or mentioned.