n the 1560s Jean De Castro decided to leave his native Liège to live in Antwerp. In the second half of the 16th century this Flemish port on the North Sea had developed into a cosmopolitan trade centre and a cultural mekka of international fame. Though wracked at that time with deep-seated political and religious problems caused by the Spanish oppression and the rise of Protestantism, Antwerp would uphold its artistic aura until well into the 17th century.
One of te main reasons for its flourishing cultural life was the great number of potential loyal patrons which lived in Antwerp. Rich foreign traders in particular, who had come to reside in the city, were keen to support artists; the possession of art, and actual connections in the artistic world suited well their aspirations and status as wealthy, tasteful world citizens (e.g. Gillis Hooftman, the members of the Genoese Nation). In 1567 the Florentine historian Lodovico Guicciardini described the colourful impact of these foreigners on Antwerp life:
The poet Guillaume De Poetou sang the praise of the merchants in Antwerp and their beneficial influence on the city's life in his Hymne de la Marchandise.
Antwerp must have appealed to De Castro in other ways as well. In the 16th century several music printers were active in Antwerp, headed by Tielman Susato and the associates Jan De Laet and Hubert Waelrant. Moreover, the city housed several other composers such as Séverin Cornet, Hubert Waelrant, Gerard Van Turnhout en Noé Faignient who secured a living in Antwerp either through an official musical position at the cathedral or the protection and financial support of the rich trading bourgeoisie. De Castro may also have been encouraged by the example of Orlandus Lassus, who fourteen years earlier, in 1555, had published his 'Opus 1' in Antwerp with the help of an influential merchant.
In 1569 Jean De Castro had his first volume printed at the firm of the Antwerp music printer, Elisabeth Saen, the widow of Jean De Laet. His first individual volume, Il primo libro de madrigali, canzoni e motetti a tre voci, gave immediate evidence of two characteristics which would remain typical for the whole oeuvre of the composer: his preference for three-part music (see Table I) and the insertion of a dedication to a patron with whom he had usually become friendly (see Table IV). Contrary to most of his colleagues who mainly published their music while comfortably being in the service of a church or court, De Castro seems to have been compelled over and again to look for a new patron for each new volume (he published over thirty music books). Most of his protectors he met in the élite world of prominent politicians and wealthy merchants in Antwerp, Lyons, Cologne and Düsseldorf.
De Castro addressed his Il primo libro to Giovanni Giacomo Fiesco, a nobleman-merchant belonging to the extremely influential Genoese Nation in Antwerp, an association of traders which played a crucial role in the city's artistic life.