《魏书·列传·卷七十》
另敕元谭西到军都关，北据卢龙塞，据此二险，以堵塞敌人出入之路。
别敕谭西至军都关，北从卢龙塞，据此二嶮，以杜贼出入之路。
Another imperial decree ordered Yuan Tan to go west to Junduguan Pass and north to occupy Lulongsai Pass. By holding these two dangerous passes, he could block the enemy's passage in and out.