3D Primitives and Conversions - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 152

• Close / Undo : When specifying points, the Close option closes the wall
and the Undo option cancels the last point, like the PLINE command.
• Arc / Line : When specifying points, Arc changes to mode Arc to add
arcs to the path. By default, arcs are continuous with the additional op-
tions Direction and Second Point , allowing directional changes. Line
changes back to mode line.

Note

For complex paths, it is better to draw a 2D polyline and then apply the Object
option.