What is the most virtuous location for Ribat (frontier guarding)?

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The best Ribat is staying in the frontier most feared due to the greater need and the more beneficial nature of one's presence there. Imam Ahmad stated that the best Ribat is the one most arduous in hardship. Furthermore, any city that serves as a stronghold for the Muslims, such as Damascus, is considered a place where a man should settle with his family. The land of Ash-Sham (Greater Syria) is the land of the Gathering (Hashr), and Damascus is a place where people will congregate if the Romans prevail.