Battle of Tong Pass

Background
After the defeat at Chibi and the subsequent loss of southern territory to Wu, Cao Cao wanted to annex the lands to the west. With the Yangzi river providing a good natural defence for the southern territories and the strong alliance of Shu-Han and Wu, the oblique approach through the mountains to the west was a safer option.

Although the lords of the Liang province had accepted Cao Cao's state, they could be called truly loyal supporters and Cao Cao's influence their was fairly minimal. In 208 A.D., just before Cao Cao attacked south, Ma Teng one of the more powerful lords in the west had accepted the position of Minister of the Guards and over 100 of his clansmen had been relocated to Ye city as hostages, his son, Ma Chao had assumed his troops and remained in Liang province.

The Battle
Cao Cao dispatched Zhong Yao and Protector of the Army Who Subdues the West Xiahou Yuan to march through Liang province and seize Hanzhong from Zhang Lu.

Fact vs Fiction
Historically...