The occupation of the whole of the soil of Argentina by white colonists is quite a recent event. The second half of the nineteenth century was characterized by a rapid territorial expansion, and over more than half the country the expression "new land" must be taken literally. It is only one generation since it was taken from the Indians. There can be no question here of tracing the history of the relations between the white population and the free Indians of the Chaco and the Pampa. The most formidable of these were, in the north, the Abipones and the Tobas. On the Pampa, the foes of the colonists were Indians of Araucanian descent, Ranqueles, Pehuenches, etc., who came down from the mountains and took to horses. At the close of the eighteenth century the frontier of Buenos Aires was on the nearer side of the Salado, and was bordered on the south-east and north-west by the fortresses of Chascomus, Monte, Lobos, Navarro, Areco, Salto, Rojas, and Melincue. The proposal of D'Azara to extend it as far as the Salado was not carried out, and it was not until 1828 that there was a fresh advance westward.[5] [5] _F. de Azara, Diario de un reconocimiento de las guardias y fortines que guarnecen la linea frontera de Republica Argentina_ (1796, Coll. de Angelis, vol. vi.). The documents collected by de Angelis show clearly that there had been some idea in the middle of the eighteenth century of occupying the whole plain to the east of the Sierra de Tandil. These ideas of expansion, of which D'Azara's plan is another instance, were interrupted by the Revolution (_Diario de D. Pedro Pablo Pabon_, Coll. de Angelis, iv. etc.). The new frontier, which would not be altered until 1875, passed by Veinte Cinco de Mayo and Blanca Grande, at the north-western extremity of the Sierra de Tandil. It included the entire region which lies between the Sierra de Tandil and the lower Salado, where the village of Tandil had been established in 1823. In addition, a line of forts stretched from Blanca Grande in the south-west to Bahia Blanca. The expedition sent in search of a port south of the mouth of the Plata had not found any nearer site that was suitable. But Bahia Blanca was to remain an isolated advance post until 1880, sharply separated from both the colonized zone of the Pampas and the establishments on the Patagonian coast.