He also wrote a small number of other religious works. Other similar books were to follow that aimed to covert the Basques to Protestantism. The closing years of the 16th century see another publication, this time from the South, of a collection of proverbs written in the Biscayan dialect called "Refranes y sentencias" by an unknown author. However, by this time, the centre of Basque literary production had firmly established itself to the north of the Pyrenees, in Lower Navarre and the French provinces of Labourd and Soule, where it would remain for several centuries. Although dialectal differences are clearly visible in these early texts, it is also clear that the differences in the 16th century were considerably smaller than they are today. In amongst the trickle of smaller religious works the Counter Reformation movement, which in the Basque Country had its centre in Sare, Soule, produced one of the most notable works of the 17th century, This was a religious publication, called "Gero", the preachings of Pedro Agerre (better known as "Axular") but in literary form, published in 1643. Although he was born in Urdax in Navarre and working in Soule, he wrote in Lapurdian, which by then had established itself as the most prestigious form of Basque. Other important works of this century were:   Although Gipuzkoan and Biscayan enjoyed some status as literary dialects, Lapurdian was by far the most commonly used dialect of the 17th century. Some referential figures of 20th century Basque literature are Telesforo Monzon, Salbatore Mitxelena, Gabriel Aresti, Nikolas Ormaetxea, Txillardegi (pen name of José Luis Álvarez Enparantza), Joxe Azurmendi, Ramon Saizarbitoria, Bernardo Atxaga, or Joseba Sarrionandia. In addition, there are many Basque writers who have written in Spanish: Blas de Otero, and Gabriel Celaya. In the 20th century, the Spanish Civil War halted all Basque cultural and literary production for almost two decades. The most-affected domain was that of language and the creation of texts in Basque. The bulk of Basque writers died or escaped to exile, where they undertook some attempts to revitalize literature by writing books or launching magazines of limited circulation. However, some works were not even published during that period.