The cellar walls were about to collapse and take the whole house with them.  The load-bearing walls in the middle of the house were made from one course of bricks.  Those bricks and that mortar were 120 years old, and both were eroded.  If you touched the brick, it turned to dust.  Parts of the wall had already begun to compress, because the mortar was falling out.

Someone had removed parts of the brick wall and had put in 4"x4" posts to support the original wooden beam.  One had so much weight on it that it was curved.  Right next to that, there was a 4"x4" post that had shrunk so much that it was loose.  Some of these wooden posts actually dented the original wooden beam, because the weight was no longer spread out along the old brick wall, but rather it was concentrated in 4"x4" spots on the beam.  Did I mention that a plumber actually cut the beam completely to make way for a pipe?  This left the two beams unsupported in four spots.

The exterior field stone walls weren't much better.  We had to rebuild the basement walls, immediately!

Before we could tear down the old brick walls, the house needed to be supported.  We built temporary beams with adjustable lally columns — on both sides of the brick wall — to support the first floor, second floor and the roof.  Just to be safe, we even put posts directly under the beam where the brick wall had just been removed.  We did this for extra support, while the concrete for the massive footings took more than 2 weeks to dry;  some of those bases of steel-reinforced concrete were 36" x 36" x 18" deep.  Then we put in 6" steel I-beams to support the house permanently.  (In the photos, the I-beams have foam on the bottom edges so no one bumps his head.)

Since this house is a "center hall colonial", there are two sets of these load-bearing interior walls in the basement.