Most presumably immediately afterwards he married Catalina de Bayona, from Medina del Campo, the eldest of the daughters of the court butcher's supplier, owner of a considerable fortune, which provided Zárate a dowry of three thousand ducats.
When the partition of his assets was carried out, Agustín received the sum of 564,525 maravedis, distributed in household furniture, silver objects and, mainly, income titles in the jurisdiction of Valladolid and the nearby country.
Although the education of Zárate did not formally go beyond an elementary level, it is evident, through his writings, that he cultivated the reading of humanistic works, in accordance with the prevailing intellectual current at the beginning of the 16th century.
[5] The enormous amount of gold and silver collected in Hispanic America since its discovery and the loose control over the economic interests of the Crown motivated the dispatch of officials with broad powers, in charge of putting order in the fiscal management of the colonies.
Zárate was an officer with good experience in court affairs and was chosen by the ruling prince (later king) Philip II of Spain for auditing the administration of the Royal Treasury in South America in the provinces of Peru and Tierra Firme.
Thus in August 1543 Zárate resigned his post as secretary of the Council of Castile and was charged as contador general for these territories with a salary of 800,000 maravedis per year plus a refund of costs of 100,000 marvedis, four black slaves and a given amount of goods free of taxes.
[5] His mission included also reviewing the work done by the Peruvian governor Cristóbal Vaca de Castro, taking care that the Crown taxes (generally equal to one fifth of any income) and other rights were paid in full.
[5] On that ship traveled also Diego Martín, cleric, butler to Hernando Pizarro, who was charged of the interests of his lord in Peru and who carried out propaganda action spreading a negative image of the viceroy in favor of the Peruvian encomenderos who were contrary to the enforcement of the New Laws.
[5] In revising the accounts of the royal treasury in Lima, Zárate noted that they were “taken without keeping in them the style and form and good order” so that he decided to undertake anew the examination of all the records, since Francisco Pizarro's conquest expedition some 15 years before.
In the pursuit of order, the judges of the Real Audiencia decided to defend the encomenderos' position and set up a special court, which pronounced the removal of the viceroy by exiling him to Spain with the general consent of the local Spanish community.
[5] During the Viceroy's trial, Zárate, who had no direct intervention in the uprising, was called as a witness and stated he heard many people, both Spanish and indigenous, complain about the manner in which the representative of the crown governed.
In order to safeguard his own image before the Spanish justice, Zárate signed a letter of protest in September 1544, stating that anything he did or would do in relation to the imprisonment and exile of the viceroy was caused by "just fear and dread”, motivated by the repression against those who were faithful to the king.
To notify the order to undo his army to Gonzalo Pizarro, who was based in Cusco, the Real Audiencia sent Zárate as one of the delegates «for being a servant of His Majesty and a man of good understanding».
[5] At the end of August he embarked on two ships the valuables he had collected for the crown, completed his auditing work in the Tierra Firme province and finally left South America on November 9, 1545.
Following a strong storm, the ship carrying him was wrecked in the Caribbean Sea and Zárate extended his journey to Mexico City where the local fiscal auditor asked him to bring to Spain the money he had collected as the outcome of his own financial audits.
[9] Lydia Fossa, scholar of American colonial literature, regards the Historia as an example of a 16th century best seller since it was published multiple times: in Spanish in 1555 and 1577 (second edition, modified); in German, French and Italian in 1563, in English in 1581.
It is composed of seven books: the first four recount the period from Francisco Pizarro's preparations for the exploration of the region to the arrival of Zárate, while the last three detail what happened in Peru from 1544 to 1550 and are written (especially the fifth, whose events the author witnessed) with great realism and dramatic intensity.
[12] According to the Real Biblioteca (Royal Library) the Historia has always been praised as a work of recognized literary quality, reprinted in Venice in 1563 and in Seville in 1577 and also translated into English, French, Italian and even German, proof of its worth.
[3] For Raimundo Lazo, Spanish literary historian, Zárate constitutes a case “whose singularity imposes its clear differentiation from the group of chroniclers of colonial Peru”.
[13] For Fernandez and Tamaro, Zárate “was a methodical writer and good stylist; although his book was not very original it enjoyed high prestige and was translated into Italian, English, French and German.
Almost all the citations refer to classical authors such as Horace, Seneca, Ovid and the "divine" Platon, whom Zárate follows in the myth of Atlantis to explain the origin of the primitive settlers of the American continent; he also quotes the Neoplatonic philosopher Marsilio Ficino.
He must have also used the letters and reports received form his nephew Polo de Ondegardo, who remained in Peru, but it is nevertheless difficult to understand how Zárate could study in a single year the subject of the Incas' religion, which he includes in his first edition.
A law published in 1558 increased control on all printed material and manuscripts and introduced the death penalty and confiscation of all wealth for those who retained or sold books condemned by the Inquisition.
Moreover, this chapter reports that the Andean Natives used to compare the miter worn by Christian bishops to a similar headwear found on pre-Incan statues (perhaps dating back to the time of the Tiahuanaco culture).
Finally chapter 12 attributes to the Andean Natives the belief in the resurrection of the flesh, a testimony to which Inca Garcilaso de la Vega was to attach the greatest importance.