Evidence of Martin’s claim that “Moscow’s master plan of 1775 called for the wall of the White City to be replaced with the Boulevard Rings, work on which began in earnest under Paul I and was completed under Nicholas I. In substituting a tree-lined public promenade for a militarily useless rampart that obstructed the circulation of people and fresh air, Moscow followed the same model as the boulevards of Paris and later, the RIngstrasse of VIenna in the 1860s. The outer ring of fortifications, the Earthen Wall, was demolished in 1816-30 to make way for the Garden Ring. Only the Kitai-Gorod Wall remained, to be razed at last in the 1930s.” (p. 7)
The observer can see here the tree lined ring that Martin is describing in his text. A few of the other rings are also visible, one outside of this one highlighted and one inside closer to the center.