Sentence:  A generation ago Chien-ch'ang was perhaps the least known part of all China to the outside world. About the middle of the thirteenth century the Mongol, Kublai Khan, acting as general of the forces of his brother, Genghis Khan, went through here to the conquest of Tali, then an independent kingdom in the southwest, and the <WSD>untiring</WSD> Venetian following in his train noted a few of the characteristics of Caindu, the name he gave both to the valley and the capital city. 
Meaning of the word marked with <WSD> tags:  Unfailing; resolute.