INTRODUCTIONBetter known in his own day as Bavarian Chancellor, Johann Georg Herwart von Hohenburg (1553-1622) was also patron and scholar of major significance. More than a scientific intermediary who spread ideas of others,1 Herwart won renown for his original work in several areas of study. His publications and surviving papers testify to his talents as a connoisseur of law and ancient languages, mathematician and chronologer,2 while his extensive correspondence with many of Europe's leading luminaries confirms his place as pivotal figure in Republic of Letters. Herwart was praised by Tycho Brahe (1546-1601) as extraordinary man excellently well versed in mathematics.3 In letter to Joseph Scaliger (1540-1609), Tycho asked dean of chronology to consider an eclipse that Herwart had calculated to revise record of history. Convinced that real references to heavens had been couched in rhyme and verse of ancient Greece and Rome, Herwart harboured habit of plotting eclipses from early poetry. was his eclectic chronology, in fact, that first brought Herwart into contact with his favourite client and fast friend, Johannes (1571-1630). Herwart exchanged more than ninety letters with over course of nearly fifteen years.4 Their vibrant discourse involved variety of topics and good turns. While their early correspondence explains why Herwart first called on Kepler, it also reveals rising star in astronomy secured support of powerful and worldly patron.Despite his relative obscurity in secondary literature, Herwart was scholar in his own right who played an important role in trajectory of Kepler's career. Intellectually, Herwart is described by some as a sober thinker,5 whose objections urged to reconsider his ideas more objectively.6 Others regard Herwart as an unrelenting client who led to reluctant philological reflections on obscure passages in Lucan, Manilius and others.7 While complained privately about great pains he took to appease his patron,8 it is clear that Herwart served as sounding board for Kepler, encouraging his client to share his ideas and interests openly.9 When they fathomed field of optics, for example, oudined his opinion that the doctrine of Copernicus was secretly contained in Euclid's Optics}0 At critical points in career of Kepler, Herwart advised and endorsed his client to others. As descended into misery during his final turbulent years as District Mathematician in Styria, Herwart brought his first book, Mysterium cosmographicum (1596), to wider attention of mathematical community. When sought employ of Tycho, Herwart counselled him carefully. He duly dissuaded from associating with Nicolaus Reimarus Ursus (1551-1600), whom Tycho had recently replaced as Imperial Mathematician. In letter to Kepler, Herwart expressed surprise that had met with Ursus in Prague. wonder, Herwart announced in alarm, how you could still associate with Ursus so closely.'2 To support succession of after sudden death of Tycho in 1601, Herwart wrote to High Councillor of Holy Roman Emperor. It is in best interests of His Imperial Majesty and Republic of Letters to keep in Prague, Herwart wrote, referring to new tables begun by Brahe that only Kepler could complete.'3 To add leverage to his appeal, Bavarian Chancellor suggested prospect of losing to local academy in Lauingen, where Philipp Ludwig (1547-1614), Count Palatine of Neuburg, had recently invited to work.In following essay, I focus on place of Herwart as patron and author in Republic of Letters. Herwart supported intellectual endeavours of his clients, in part, to promote his own calling in chronology. While he aided revolutionary astronomy of Kepler, Herwart peppered his prize client with requests to calculate eclipses that helped him rewrite history. …