73 capital... I had walls, castle, but not the next one up (arsenal I think?) and I didn't have The Kremlin, but I took the Liberty policy of +33% city defense. My record so far is 149 in a big capital with every building/wonder/policy that juices up the defense. The opponent's Mech Infantry and bombers were dying when they struck it, but he spammed them and had ranged attacks... that was back when I was a "noob" and I ended up losing the game cuz I didn't know what I was doing.
Who was it against? 149 is a huge defense but I have seen close I know I have.