Filmer's "Observations concerning the Original of Government upon Mr Hobbes's Leviathan, Mr Milton against Salmasius, and H. Grotius' De jure belli ac pacis" appeared in 1652. In line with its title, it attacks several political classics, the "De jure belli ac pacis" of Grotius, the "Defensio pro Populo Anglicano" of John Milton, and the "Leviathan" of Thomas Hobbes. It is the source for the famous quotation from Hobbes, asserting that people "as mushrooms... sprung out of the earth without any obligation one to another." The pamphlet entitled "The Power of Kings, and in particular, of the King of England" (written 1648) was first published in 1680.