The rich man's wealth is his strong city, and as an high wall in his own conceit.
The rich man's wealth (is) his strong city (Proverbs 10:15 ), and as an high wall in his own conceit - in contrast to the righteous man's "strong tower," "the name of the Lord," in which he is "set on high" in safety (Proverbs 18:10). It is infinitely better to "trust in the living God" than "in uncertain riches" (1 Timothy 6:17).