According to Wikipedia:
Eventually, Florence came to regret Dante's exile, and made repeated requests for the return of his remains. The custodians of the body at Ravenna refused to comply, at one point going so far as to conceal the bones in a false wall of the monastery. Nevertheless, in 1829, a tomb was built for him in Florence in the basilica of Santa Croce. That tomb has been empty ever since, with Dante's body remaining in Ravenna, far from the land he loved so dearly. The front of his tomb in Florence reads Onorate l'altissimo poeta—which roughly translates as "Honour the most exalted poet". The phrase is a quote from the fourth canto of the Inferno, depicting Virgil's welcome as he returns among the great ancient poets spending eternity in Limbo. The continuation of the line, L'ombra sua torna, ch'era dipartita ("his spirit, which had left us, returns"), is poignantly absent from the empty tomb.