Cities built on mounds were walled cities built on the ruins or debris of previous settlement—as such cities were customarily built. Hazor was the only one of those cities that Joshua set on fire.

Which Joshua did burn may be omitted from explicit mention in translation, since the phrase except Hazor clearly implies that Joshua and his army did burn that city. In fact, in light of verse 11, this verse may be translated, “However, Joshua and his men did not burn any of these cities. They left them standing on the mounds where they were built.”

Quoted with permission from Bratcher, Robert G. and Newman, Barclay M. A Handbook on Joshua. (UBS Helps for Translators). New York: UBS, 1983. For this and other handbooks for translators see here .