שמות, פרק ל״ו, פסוק כ״ז

As the construction of the Tabernacle's walls progresses, the builders move toward the back of the structure, which faces the west. To form this rear section, they set up six upright boards. Because each individual board measured one and a half cubits in width, placing them side by side created a continuous stretch that covered exactly nine cubits. Together, this sequence of wood formed the main body of the western wall.