A few weeks after that, he was in charge of briefing the teams that were about to travel through the Stargate to the new Alpha Site (SG1: "The Serpent's Lair"). Some months later, he was temporarily reassigned to command SG-1 while Colonel Jack O'Neill succumbed to the download from the Ancient's Repository of knowledge. (SG1: "The Fifth Race") During the Goa'uld negotiations in 1999, Castleman lead the base defense force in removing all weaponry and assisted in general security of Stargate Command. (SG1: "Fair Game")