The crossing of the Jordan River is remembered not only by a monument on dry land but also by a second memorial built within the riverbed itself. A completely new set of twelve stones, entirely distinct from those carried out to the Israelite camp, was placed in the water [רש״י, מצודת דוד, מלבי״ם, ביאור שטיינזלץ].
The motivation behind this second monument is a matter of discussion. While some suggest Joshua acted upon an unrecorded command from God [רד״ק], others believe it was Joshua's own initiative. He wanted to establish an additional sign within the river to mirror the monument built on land [אברבנאל].
The placement of these stones was directly tied to the priests standing in the river. Since the priests had not yet moved, the stones were not set directly beneath their feet, but rather right next to where they stood [רד״ק]. Another perspective suggests they were placed as a direct replacement for the ground the priests occupied [אברבנאל], or that they were set in the exact same spot immediately after the first set of stones was pulled out from under them [מלבי״ם]. In any case, the stones marked that specific location [מצודת ציון].
The establishment of this riverbed monument served several purposes. Practically, it may have provided a solid surface to prevent the priests from sinking into the mud [אברבנאל בשם רש״י]. It also acted as a public marker, showing the nation the exact area where the waters miraculously stood like a wall [רלב״ג]. Beyond the physical event, the two sets of stones carry a deep symbolic meaning. The twelve stones taken out of the Jordan represent the tribes of Israel rising into the land to remain there. Conversely, the stones cast into the depths of the river represent the surrounding nations who will be removed and cast out of the land in their place [אברבנאל].
When placing these stones, Joshua did not simply toss them into the water. He built a large, tall structure designed to stand out above the surface, ensuring it would be visible from the riverbank [אברבנאל]. Alternatively, some understand that the stones formed a mound on the riverbed, remaining permanently hidden beneath the flowing current [ביאור שטיינזלץ]. Regardless of its exact appearance, the monument was established to endure forever. The prophetic record notes that it remains there permanently, allowing readers in every generation to acknowledge its lasting presence [מצודת דוד].