The Obelisks of the Mausoleum of Augustus are a pair of Aswan granite obelisks that once stood in front of the Mausoleum of Augustus in the Campus Martius in Rome. They are a little over 14 meters high and as they are uninscribed, it has been presumed they were made during the Roman period.  The pyramidion was cut away to make room for some kind of ornament. 
They are not mentioned by Strabo in his description of the mausoleum, though Ammianus Marcellinus later mentions them in the 4th century. It is presumed that they were placed there at a later period, perhaps at the end of the 1st century AD. In the Middle Ages, the mausoleum was used as a fort, and the two obelisks, which had fallen down, were buried. 
One of these obelisks (Esquiline Obelisk) was excavated in 1519 and was erected in Piazza Esquilina behind S. Maria Maggiore in 1587 by Fontana. The other (Quirinale Obelisk) was discovered around the same time, but was then reburied for unknown reasons. It was excavated in 1781 and under Pius VI three fragments of the obelisk were erected at Piazza del Quirinale between the Quirinal Dioscuri. The ceremony of inauguration of these obelisks included exorcism and praise of the victory of Christianity over paganism.

See also Roman Monuments and Roman Obelisks