Jat-Krula

The Maginot Line, otherwise known as the Maginot Sphere, was a Forerunner defensive line that protected the Forerunner inner colonies. It divided what the Forerunners were able to protect from what they had to leave to the Flood. Its precise boundary is unknown; however, Earth was not inside it and neither were most of the worlds the Librarian visited in her duties. For a long time, the Didact worked in the Maginot sphere, frequently sending transmissions from it to the Librarian asking her to retreat behind it to where the Didact said their fleets could protect her. The sphere was breached when the Flood made a massive attack on it, led and commanded by the rampant Forerunner AI Mendicant Bias.

Although the nature of the Maginot Line was not elaborated upon in the Terminals, Line Installation 1-4 may well be part of the Line. This is supported by the Installation's name, as well as its function - preventing ships passing through a certain point using a weapon that can fire into slipspace, as well as serving as a Flood research facility. In addition, Frank O'Connor commented on the name that "fans of the terminals will probably figure it out", implying that the reference to a "Line" is linked to the story told in the Terminals, where the Maginot Line was first mentioned.

Naming
"Maginot Line" was not the actual name used by the Forerunners to refer to the defensive perimeter. The Forerunner records describing the line were discovered using translation software so advanced that it incorporated idioms from the reader's own culture, thus when Forerunner terms cannot be directly translated, the software replaced them with human terms of more or less equivalent meaning. Thus, terms such as "Eden", "fairy tale" and "Maginot Line" became the default usage in Forerunner terminals and transmissions when read by humans. These words appear in brackets in the Terminals.

The translated name is a reference to Maginot Line, a World War II French line of fortifications, meant to repel an anticipated assault from Germany. Though it dissuaded a direct attack, German tank units maneuvered around the fortifications, bypassing most of them altogether, making the fortifications mostly useless and leading to the fall of France. When the Allies retook France, the Germans manned them, but again the majority of the lines were bypassed.