From the time of the Reformation, most of the leadership of the Reformed Church of Hungary was trained outside Hungary. In the sixteenth century, the Hungarian Reformed ministers studied in Wittenberg, where a "Coetus Ungarorum" was in existence until their expulsion in 1592. Matyas Devai Biro, Istvan Szegedi Kiss, Peter Meliusz Juhasz, Gaspar Karolyi, and hundreds of others were alumni of Wittenberg University and members of the Hungarian student organization "Coetus Ungarorum." After the Hungarian Reformed students were forced out of Wittenberg by the intolerant Lutheranism of the age, they began to attend the German universities of Heidelberg, Altdorf, and Frankfurt-an-der Oder. The uncertain period of the Thirty Year War, however, soon ended the possibility of studies in Germany. Heidelberg University was destroyed in 1622 and very soon a new period began in Hungarian church history which lasted for more than three-hundred years: "Peregrinatio Belgica," as it was called in the seventeenth century. The first Hungarian theological students arrived in Holland in 1623; most likely this date should be considered as the beginning of the very significant Dutch and Hungarian Reformed connections.