"In Defense of Trump, Some Point (Wrongly) to Vatican Walls." The NYT story goes on to say "Some of the walls in Vatican City were built in the ninth century by Pope Leo IV in an attempt to protect it from attacks by pirates and other marauders, historians said." The source for the article is a Georgetown (Catholic) historian, who asserts that the walls do not entirely enclose the city state.
Truth: The main wall of the Vatican was built in response to enemy incursions, and Muslim incursions to boot! : "The Leonine Wall, which defines the Leonine City, was constructed by Pope Leo IV following the sacking by Muslim raiders of Old St. Peter's Basilica in 846. Built from 848 to 852 as the only extension ever made to the walls of Rome, this three-kilometre wall completely encircled the Vatican Hill for the first time in its history." - wiki
The main argument supporting Trump can be found here.