Who were the largest landowners during within the midieval societies

When discussing Medieval European society, feudalism is often the first topic.

The feudal system was a type of social order which, over a period of several hundred years, spread across Europe. Feudalism was similar to a contract in which individuals pledged their loyalty and services to a lord or person of higher rank. The loyalty was rewarded with the promise of protection and the chance to occupy land.  

In Medieval Europe, the monarch was at the top of the feudal system. Usually a king, the monarch, would grant land called fiefs to tenants-in-chief, who were usually lords.  

The lords granted land to sub-tenants, which usually included knights.  

And at the bottom of the feudal system were the peasantry. Sub-tenants often granted land to peasants, who were also known as serfs.

a. poison gas was sprayed over battlefields by airplanes to weaken enemy positions before major attacks.

the exodus of these people from constantinople contributed to the revival of greek and roman studies, which led to the development of the renaissance in humanism and science. byzantine emigrants also brought to western europe the better preserved and accumulated knowledge of their own greek civilization