Despite having been destroyed by Russian forces twice (in 1525 and 1654), the city continued to grow and following the Union of Lublin it became a major administrative and trade centre, as well as a seat of a powiat ("county" office and court).
På trods af at Mazir var blevet ødelagt af russiske styrker to gange (i 1525 og 1654), fortsatte den med at vokse og efter Lublinunionen blev den et vigtigt center for administration og handel, samt et sæde for en powiat (dansk: ~ amt).