Legatio is the international online open source journal hosted by the Polish Academy of Sciences' Tadeusz Manteuffel Institute of History, Warsaw, in conjunction with the Premodern Diplomats Network. The journal invites contributions from suitably qualified scholars in two categories: articles and critical editions of primary sources. Any submissions will be subject to a double-blind peer review before publication. The journal will also publish book and exhibition reviews, conference reports, and notices relevant to the field of study.
You can find Legatio here
Update on Legatio from Laura Mesotten