Which important property did Mendeleev use to classify the elements

Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?

Mendeleev used atomic weight as the basis of classification of elements in the periodic table. He arranged 63 elements known at that time in the periodic table on the basis of the order of their increasing atomic weight. At some places he ignored the increasing order of atomic weights to place the elements having similar properties together.