There were soldiers from different armies, a white walker, a direwolf and players dressed up like the HBO show's main characters.
"Say hello to Jon Snow and his DireWolf ghost..Shout out to @brittharppete for the costume and my lovely wife (@kayy.harper) for the make up! #gameofthrones," Harper wrote on Instagram.
Harper shows off a mean growl in a photo with Werth as his teammate holds 'Longclaw,' the sword made of Valyrian steel used by Snow on the show.
"October baseball is coming," the Nationals wrote on a Twitter post, showing off the costumed squad.
The Nationals left New York after winning three out of their four games against the New York Mets. Washington began its three-game series against the Phillies on Monday night. The Nationals wrap up the regular season with a four-game series against the Pittsburgh Pirates starting on Thursday.
The Nationals have already clinched home-field advantage in the National League Division Series, which begins this weekend.