《元史·本纪·卷二十七》
因诸王怯伯使者多次入朝，发兵防宁北口及卢沟桥。
以诸王怯伯使者数入朝，发兵守北口及卢沟桥。
<number>. Due to frequent visits from envoys of King Qiebo, sending troops to defend the Ningbei Pass and Lugou Bridge.
<s>[INST] Explain the meaning of this Classical Chinese passage in English: 以诸王怯伯使者数入朝，发兵守北口及卢沟桥。 [/INST] <number>. Due to frequent visits from envoys of King Qiebo, sending troops to defend the Ningbei Pass and Lugou Bridge.</s>
Explain the meaning of this Classical Chinese passage in English: 以诸王怯伯使者数入朝，发兵守北口及卢沟桥。
user
<number>. Due to frequent visits from envoys of King Qiebo, sending troops to defend the Ningbei Pass and Lugou Bridge.
assistant