What is the section of wall built in advance to determine wall lines and elevation called?

The section of wall built in advance to establish the wall lines and elevation is referred to as "the lead." This initial segment is crucial in masonry work as it serves as a reference point for the construction that follows. By ensuring that the lead is correctly aligned and at the proper height, masonry workers can lay bricks or blocks consistently, maintaining the desired dimensions and structural integrity of the entire wall.

This practice is particularly important in masonry because any deviation in the lead can lead to issues with alignment, aesthetics, and overall stability. The lead enables masons to gauge the rest of the wall accurately, allowing them to check for level and plumb as they proceed. In essence, the lead acts as a guide for the entire masonry project, ensuring that all subsequent work adheres to the established lines and levels.