מלכים א, פרק ז׳, פסוק מ״ו

Creating the massive vessels for the Temple was an engineering marvel that demanded highly specific geographical conditions and the personal oversight of the king himself. The casting of these items took place in the flatlands of the Jordan River [מצודת ציון, רלב״ג, רד״ק]. King Solomon took a direct role in this monumental task for several reasons. Because the polished copper was incredibly valuable, he chose to personally supervise the operation to ensure its safety and quality [מלבי״ם]. Furthermore, the king's presence served to honor the work being done for God's house while motivating the laborers to work efficiently. Using his distinct wisdom, Solomon was able to identify the exact location where the soil conditions would guarantee a successful casting [נחל שורק, חומת אנך].

The physical process required melting the copper and pouring it into molds [רש״י]. However, the Temple vessels were so enormous that it was impossible to create standard molds for them in a typical workshop. To solve this, engineers dug the shapes of the vessels deep into the thick, clay-like earth, pouring the molten metal straight into the ground [רש״י, מצודת דוד, רלב״ג, רד״ק]. The specific area chosen for this work, located between Succoth and Zarethan, provided soil that was thick, moist, and of a high enough quality to form both the furnaces and the complex molds needed for such giant creations [מלבי״ם, רד״ק, ביאור שטיינזלץ].

Despite this careful setup in the Jordan valley, this location was reserved specifically for the items made of the highly valued polished copper. Other large items crafted from basic copper were likely cast right in Jerusalem. This practical decision saved the workers the tremendous difficulty of transporting such heavy, massive objects over long distances [מלבי״ם].