Grid Thirteen by Twenty-Four, on the planet Sigma Octanus IV, was a location deep in the jungle on the planet, just outside the outskirts of the capital, Côte d'Azur. Though covered by dense foliage, it was also home to a river and several rocky embankments, which serve well to conceal bases.
In the early 2500s, a meteor crashed in this Grid. Unbeknown to the Human colonists, the meteor contained Forerunner artifacts. The colonists took some of the artifacts from the meteor, and put them in the Côte d'Azur Museum of Natural History 
In 2552, during the Battle of Sigma Octanus IV, the UNSC Marine Corps set up a Firebase in Grid 13 x 24, Firebase Bravo. They hoped the embankments would hide the base. Unfortunately, they were wrong. The Covenant ambushed the base and destroyed it, slaughtering most of the Marines when a force of Unggoy, Kig-Yar, and Mgalekgolo overwhelmed the group. A lucky band of survivors, led by Corporal Harland, managed to make it all the way to Alpha HQ, where they were relieved by the Spartans who managed to drive the Covenant away.