article_snippet.sent: The idea for underground cities came during the Byzantine-era when residents used residents as hideouts when threatened by invasion by the Persians, Arabs and Seljuq Turks.
article_snippet.sent: The idea for underground cities came during the Byzantine-era when residents used residents as hideouts when threatened by invasion by the Persians, Arabs and Seljuq Turks. '
article_snippet.sent: The idea for underground cities came during the Byzantine-era when residents used residents as hideouts when threatened by invasion by the Persians, Arabs and Seljuq Turks.