The quote by Kelley Armstrong in her book "Omens" suggests that if the Romans had the same defensive mechanisms as the human brain, their cities would have been much better protected. This comparison highlights the brain's ability to strengthen itself against threats and vulnerabilities, much like how a fortified city would defend against invasions. It implies that the brain's resilience is crucial for survival and adaptation.

Armstrong's statement also invites reflection on the nature of human intelligence and evolution. Just as Romans built walls to protect their cities, the brain has developed complex processes to shield itself from psychological and environmental challenges. This metaphor emphasizes the importance of mental fortitude and adaptability in overcoming obstacles, suggesting that our internal defenses are as significant as any external ones.