Dear Tanya,

As others have indicated, most likely, your myterious pit is a privy.  I have
excavated a few here in Texas that conform to your description.  The
closeness of the pit to the house is probably because they may have used the roof  as
a way to collect rainwater and deliver it to the privy.  You usually find the
roof being use as a collection point in areas where there is not a high
quantity of annual rainfall.

I hope this helps.

Jorge Garcia-Herreros, RPA
Perennial Environmental Services, LLP