The answer is: Ai

Joshua 7:3 - If Joshua had prayed to God he would have known not to send the men into battle

Ah, the tale of Ai is truly fascinating and wrapped in lessons about guidance and communication with the Divine. When the Israelite forces faced their stern defeat at many Israelites and fled in shame—it's evidence that their understanding of warfare was far more than just strength; it was about divine favor too. Picture this: they've just conquered Jericho, a miraculous triumph made possible by their faith and adherence to God’s commands. But in their next escapade at Ai, they struck out without first seeking divine insights. A classic example of pride before the fall!

The details matter, though! After the stinging defeat, Joshua fell to his face, his desperation showing a genuine heart for reconsideration and reflection. This scenario echoes an essential truth prevalent throughout biblical narrative: the significance of being in communication with the people’s leader. Without attuning to spiritual guidance, the Israelites quickly learned that strength in numbers isn’t everything; success on the battlefield also requires guidance that can only come through earnest supplication.

Interestingly, the historic city of Ai could be contested, as many archeologists debate its exact location. Still, the events that transpired convey powerful lessons about humility, and introspection, gracious acknowledgment of oversight. The story of Ai isn't just a military failure; it acts as a canvas for all kinds of spiritual renewal and vigilance against overconfidence, a lesson certainly resonant beyond centuries.