The moon of Alexandria is so named because it is home to a massive storehouse of knowledge. Two hundred years ago, human explorers found what is believed to have been some sort of observatory that belonged to a species that used the moon as a base millions of years ago. Amazingly, the database was mostly intact. What the aliens probably thought of as incidental knowledge barely worth considering important was enough to catapult human spacefaring technology several centuries ahead. Because of the massive amount of data in the database, the planet was named Alexandria. Because there is still a wealth of classified data and technology on the jungle moon, it is protected by a massive defense fleet.
The fleet is centered around two massive Cerberus Mobile Defense Platforms, armored space stations that can unleash tremendous firepower and several wings of fighters and which can maneuver short distances within the star system. The Cerberus stations are supported by a main battle fleet that is constantly upgraded with the latest ships and technology. There is also a large force of marines on the moon itself which are ready for trouble from both external threats as well as any internal threats unleashed from ancient structures still being discovered to this day.
The fleet itself is there partially as a last resort containment measure in case something is discovered on the moon that cannot be contained. In such a situation, the fleet has orders to quarantine the planet and will open fire on any vessel trying to leave, including civilian ships trying to escape a calamity.
Alexandria, which orbits the gas giant Cleopatra, is the only human colony considered a "core world" of the Terran Protectorate that requires special security clearance to visit. Being a native of Alexandria is a fast-track into a career in military intelligence, because every native born Alexandrian passes a background check once every two years or else they face relocation to another core world, if not a prison sentence....