Scholars had originally thought that invaders attacked the city in the 7th or 8th century, sacking and burning it. More recent evidence, however, seems to indicate that the burning was limited to the structures and dwellings associated primarily with the ruling class. Some think this suggests that the burning was from an internal uprising. They say the invasion theory is flawed, because early archaeological work on the city was focused exclusively on the palaces and temples, places used by the upper classes. Because all of these sites showed burning, archaeologists concluded that the whole city was burned. Instead, it is now known that the destruction was centered on major civic structures along the Avenue of the Dead. The sculptures inside palatial structures, such as Xalla, were shattered. No traces of foreign invasion are visible at the site.