Commentary for Numbers 13:28

בצרות is an expression for strength. Its rendering in the Targum is כריכן, a term for circular fortresses, for in the Aramaic language כריך means round.

אפס כי עז העם, it is impossible to conquer the land since we cannot defeat its people. Not only are the people tough, but the cities are fortified. The inhabitants of the land, the Amelakites hate us fiercely. They will engage in a preemptive war against us so that we should not even get near their borders.

אפס כי עז העם, "However the people are tough, etc." Seeing that Moses had specifically asked them to determine if the people who inhabited that land were strong or weak, they now had to report that the people were indeed formidable. Not only that but they dwelled in heavily fortified towns. They concluded that part of their report by mentioning that they had observed giants in the land. They stated this so that the Israelites should not think that the fact that the towns were fortified revealed weakness and lack of self confidence by the inhabitants.