Trigovia

 was a city on Gallifrey. The Sapphire Towers were located there.

Norvid was visiting Trigovia when he got his call to join the Last Great Time War. When Norvid was telling the Doctor and Veeda about this, Veeda dutifully declared that "Gallifrey's cities are worth protecting" and that she was "happy to do [her] duty". (AUDIO: The Conscript)