Hi Annie,
Great that you have had a transcription from Panda. I don't wish to be a wet blanket but having looked carefully at my manipulated image of the gravestone I dispute a couple of points.
A... The curved word at top appears to be CAPI not CAPRI. I think it should probably have fullstops and read as C.A.P.I.
B...The word Grart Appears to have aspace between the first r and the a and possibly a fullstop.
Now knowing that the next word translates as Garrison things become clearer . Gr.art is probably the standard abbreviatin for a soldier associated with a heavy gun unit . I surmise in English would read as Gunner Artillary Garrison.
Why not contact the Portugese Embassy they will probably be able to tell you all about the Grave and maybe the soldier .I think they must have an equivalent of our CWGC as I have seen the same type of stone in French War Cemeteries.
Again, Good Luck ,Rog