The genitive case died out around the 3rd century AD, according to Meyer-Lübke, and began to be replaced by "de" + noun (which originally meant "about/concerning", weakened to "of") as early as the 2nd century BC. Exceptions of remaining genitive forms are some pronouns, certain fossilized expressions and some proper names. For example, French ("Thursday") < Old French juesdi < Vulgar Latin ""; Spanish es ("it is necessary") < "est "; and Italian ("earthquake") < "" as well as names like Paoli, Pieri.
the geniTIve caSE Died out arOund the 3RD ceNTurY ad AccoRdiNg to mEyER-LübkE anD beGAn to be REplacEd BY "de" + noun (whIcH oriGInAlly MeAnt "aboUT/cOncERNIng" WEakeNeD To "Of") as eaRlY aS the 2Nd CeNTUry bC exCEptionS of remaining geniTive forMs are some prONoUns certain FosSiliZeD ExPrEsSIons and SOMe proper naMes for exAmPlE frENCh ("thursDay") < Old freNch juEsdI < VULgaR laTIn ""; spanish eS ("it iS necessAry") < "est "; and Italian ("eaRTHquAKe") < "" as well as namEs LiKe paOLi pierI