Four stratovolcanoes are visible from the city, two of them active. The nearest and most active is Pacaya, which at times erupts a considerable amount of ash. These volcanoes lie to the south of the Valle de la Ermita, providing a natural barrier between Guatemala City and the Pacific lowlands that define the southern regions of Guatemala. Agua, Fuego, Pacaya and Acatenango comprise a line of 33 stratovolcanoes that stretches across the breadth of Guatemala, from the Salvadorian border to the Mexican border.