I love these lines by Auden! I think he is trying to point out how our buildings, and skyscrapers specifically reveal the strength of humanity. Architecture is something that varies so much between cultures. The more grand buildings we make, the higher our towers climb, the more value we put in our strength as a nation. Our buildings are not for us to see but for other countries to look at in awe of our power. This is mostly futile as Auden points out. It's just one big competition between countries, with little regard for the people actually constructing the masterpieces.