This is a Mauritius Pre Stamp Cover Sheet.  It was sent from Port Louis, Mauritius to Nantes, France on 3/25/1857.  It was received on 4/27/1857

What makes this letter so special is not merely its age and condition, but the postal markings it has.  To start off, it has the BLACK DOUBLE OVAL PACKET LETTER MAURITIUS marking on the back, dated 3/25/1857.  It also has a transit & receiver mark on the back for Bordeux, Paris, and Nantes, in black.  There is also a Paris transit in RED on the front, as well as an M/S 8 charged postage.  There is a wax seal on the back as well.

Please take care as this cover, while it is in fantastic shape, is still over 100 years old.