Registered Cossacks

Zaporozhian Host
Active	1572 - 1648
Country	Polish–Lithuanian Commonwealth
Allegiance	Polish–Lithuanian Commonwealth
Branch	Army
Type	Light cavalry Skirmisher
Role	Patrolling Raiding Reconnaissance Screening Shock tactics Wagon fort
Size	up to 40,000 (1649)
Garrison/HQ	Trechtymirów (Trakhtemyriv), Kiev Voivodeship
Engagements	Livonian War, Moldavian Magnate Wars, Polish–Ottoman War, Polish–Muscovite War
Commanders
Notable commanders	Petro Konashevych-Sahaidachny, Mykhailo Doroshenko, others

Registered Cossacks (Ukrainian: Реєстрові козаки, Rejestrovi kozaky, Polish: Kozacy rejestrowi) comprised special Cossack units of the Polish–Lithuanian Commonwealth army in the 16th and 17th centuries.^[1]

Registered Cossacks became a military formation of the Commonwealth army beginning in 1572^[2] soon after the Union of Lublin (1569), when most of the territory of modern Ukraine passed to the Crown of Poland. Registered Cossack formations were based on the Zaporozhian Cossacks who already lived on the lower reaches of the Dnieper River amidst the Pontic steppes as well as on self-defense formations within settlements in the region of modern Central and Southern Ukraine.