Sky trench
From Tardis Wiki, the free Doctor Who reference
Sky trenches appeared to be a form of defense used by the Time Lords to protect Arcadia. The sky trenches were thought to have been impenetrable, although a fleet of Daleks later broke into Arcadia possibly initiating the Fall of Arcadia.Arcadia (city)|Arcadia]] was protected by 400 Sky trenchs making it the safest city on Gallifrey. (WC: The Last Day)
