Unlike the first two films in the Hunger Games series, the Mockingjay two-parter did not require the production designers to create a battle arena for the terrifying spectacle that is the titular slaughter. Instead, Mockingjay’s final battle happens when Katniss (Jennifer Lawrence) storms the Capitol along with a group of rebel soldiers looking to assassinate President Snow (Donald Sutherland). Creating the environment for that final climactic scene involved building a massive, 900-foot-long set and then filling in the background with CGI thanks to what production designer Philip Messina calls the largest green screen he’d ever seen. Find out how he made it work in the clip above from the home video release of The Hunger Games: Mockingjay — Part 2, which hits digital HD today and Blu-ray on March 22.