Kazimierz Siemienowicz (, ; born 1600 – 1651) was a general of artillery, gunsmith, military engineer, and one of pioneers of rocketry. Born in the Raseiniai region of the Grand Duchy of Lithuania, he served in the armies of the Polish–Lithuanian Commonwealth and of Frederick Henry, Prince of Orange, the ruler of the Netherlands. No portrait or detailed biography of him has survived and much of his life is a subject of dispute. After contributing his expertise to several battles, Siemienowicz published Artis Magnae Artilleriae in 1650. This treatise, which discusses rocketry and pyrotechnics, remained a standard work in those fields for two centuries. Early life Lithuanian school Lithuanian literature asserts that he was born near Raseiniai in Samogitia. The family, who was relatively poor, bore the Ostoja Coat of Arms with military service traditions in the Grand Duchy. In a book dedication, he refers to himself as an "Eques Lithuanus" (Lithuanian nobleman). Siemenowicz was educated in the Academy of Vilnius. Polish school The Polish school describes his identity simply as member of the szlachta (i.e., nobility in the Commonwealth) from Grand Duchy. Some sources use the term "Polish," others describe him as "Lithuanian". Those terms should be understood in proper context: "Polish" means "of the Polish–Lithuanian Commonwealth"; "Lithuanian" from the Grand Duchy of Lithuania, a federal part of the Commonwealth. Polish historian professor Tadeusz Marian Nowak described Siemienowicz as a Polonized Lithuanian nobleman. Polish historians for the most part accept that he used the Ostoja Coat of Arms and that he was an alumnus of the Academy of Vilnius. Belarusian school The Belarusian school asserts that he was born in the vicinity of Dubrowna in the Viciebsk land, to a family of minor Ruthenian princes (knyaz) of Siemienowicz, who possessed the small tracts of land in that part of the Belarusian Dnieper-land (Падняпроўе) in the 14th–17th centuries. Some examples of lexicography used by K. Siemienowicz support this interpretation. There are no records of families with the surname Siemienowicz having the right to bear the Ostoja coat of arms and it is possible that Siemienowicz acquired the right to use the image of Ostoja in his book to facilitate its circulation. Military career As Siemienowicz wrote, he was fascinated by artillery since childhood, and he studied many sciences to increase his knowledge (mathematics, mechanics, hydraulics, architecture, optics, tactics). In 1632–1634 he took part in the Smolensk War, in the Siege