Ernica city, Alatri became a Roman town hall following the rebellion of the ernica league  against Rome in  306 A. C. rebellion in which Alatri didn't participate. Destroyed by the Gotis of Totila,  rebuilt with the name of Civitas Nova, that maintained up to the XIV sec.á 
The city fought against Enrico Vi and Federico II, until it fell in power of the Papacy in 1389. Episcopalian nead quarters from the notable boundaries polygonal ciclopiche with addition of boundaries and  quadrilateral medioevalis towers. Fulcrum of the city is the acropoli, constructions ciclopica also surrounded by boundaries with the Door Civita and the Small Door  besides the church of S. Maria , Romanesque, built toward half the XIII sec.á

The hut fašade  introduces a splendid rose window in the center, while the bell tower of the XIV sec. it is to two orders of bifore. 
The church of S. Francesco goes up again at the end of the XII sec, while the Cathedral, in which Pope's sepulchre Sisto I is preserved, it  is surrounded by an ample public park from which is possible to admire the splendid valley of the Sacco river.