From Halopedia, the Halo wiki
The John-117 Monument is a comprehensive diorama constructed to commemorate MCPO John-117's heroism during the Human-Covenant War. Beginning in 2607, the UNSC began commissioning artists to help with the construction of the monument and the museum enclosing it. All of the character, firearm, vehicle, and landscape models were created by hand, with the likenesses of each Marine based on "induction scans" and postmortems of dead Covenant troops recovered after the Battle of Mombasa.
Only the men and women who participated in the battle knew how it really looked. Based on topographical maps taken before, during, and after the fight, artists were able to precisely pinpoint where everything had to go. Architectural records recovered later provided the basis of what the buildings would look like, but it was the artists' jobs to place each point of damage accordingly. They worked fiercely to recreate the amount of damage the city sustained, from bullet holes and craters, to the chunks of missing walls and the exposed re-bars within. Completed in 2610, a documentary began to be produced, to chronicle the making of the monument, the soldiers' reaction to it, and the Museum of Humanity itself. Some soldiers would visit sites where they fought, often describing their situation at the time.
The massive diorama of the John-117 Monument is over 1,200 square feet in size and over twelve feet tall. The Human and Covenant figures were all handcrafted, each standing eight to twelve inches in height. No machines were used to construct the molds. The set and vehicles were built by New Deal Studios and the figures were supplied by Stan Winston Studio.
After filming was completed, the monument was broken up and its parts distributed to various owners. Pieces of the monument are at Microsoft's campus buildings in Redmond. The central portion with Master Chief, the Brute Chieftain, and many surrounding Brutes is kept at Bungie's studio in Bellevue. 343 Industries received their own segment of the diorama as well. At Halo Fest 2011, three chunks of the diorama were put on display (a portion with a Scorpion tank and fighting armies, a section with Hunters and Marines fighting around building fragments, and Bungie's central piece). A few other sections and pieces of the monument were auctioned off and sold in 2015 and 2016 at El Segundo, California. When 343 Industries moved out from Kirkland in 2016, they were unable to take their diorama piece into their new building, as it was not glued together and could not be safely transported. When Joseph Staten learned of this during a tour for the Halo 15th Anniversary Twitch livestream, he jokingly proposed that they carry out an elaborate raid to go retrieve the piece back.