From Wikipedia: The Cucuteni-Trypillian culture, also known as Cucuteni culture (from Romanian), Trypillian culture (from Ukrainian) or Tripolye culture (from Russian), is a late Neolithic archaeological culture which flourished between ca. 5500 BC and 2750 BC, from the Carpathian Mountains to the Dniester and Dnieper regions in modern-day Romania, Moldova, and Ukraine, encompassing an area of more than 35,000 km2 (13,500 square miles).[1] At its peak the Cucuteni-Trypillian culture built the largest settlements in Neolithic Europe, some of which had populations of up to 15,000 inhabitants.

Another periodization has been assigned to this culture that breaks it down into three main eras:.[3]
• Early: 5500 to 4600 BC
• Middle: 4600 to 3200 BC
• Late: 3200 to 2600 BC

More on the discovery of the Trypillian civilization here.

I’m not sure how to reconcile this with the widely held idea that Sumeria was the first civilization. Perhaps the Trypillians weren’t big enough.

From wikipedia: The cities of Sumer were the first civilization to practice intensive, year-round agriculture, by 5000 BC showing the use of core agricultural techniques including large-scale intensive cultivation of land, mono-cropping, organized irrigation, and the use of a specialized labor force. . . . There was little evidence of institutionalized violence or professional soldiers during the Uruk period, and towns were generally unwalled. During this period Uruk became the most urbanised city in the world, surpassing for the first time 50,000 inhabitants.