Alan Lee - Osgiliath. The old capital city of Gondor. The city straddled the Anduin River at a point approximately half way between the cities of Minas Anor to the southwest and Minas Ithil to the northeast. In the Great Hall of the city the thrones of the sons of Elendil were set side by side. In its days of glory, the city featured quays, a great stone bridge supporting houses and towers of stone, and the Dome of Stars, which housed the Osgiliath-stone, the greatest of the seven.
At the heart of Osgiliath was a great stone bridge over the river. On the bridge was a tower containing the famous Dome of Stars, which housed the city's Palantír. Osgiliath was hit hard by the catastrophic civil war of the Kin-strife. In TA 1437, the city, then held by Eldacar, was besieged by Castamir's forces. During the fighting, fire broke out, and large parts of the city were destroyed, including the Dome of Stars. The Palantír housed in the Dome was lost in the river.
The Ithil-stone was the palantír that stood in Isildur's ancient fortress of Minas Ithil placed there soon after the founding of the city. The stone was captured by the Nazgûl in T.A. 2002 when the city fell to them (being known afterwards as Minas Morgul), and was used by Sauron to entrap Saruman and deceive Denethor during the War of the Ring. It is likely that the stone was destroyed in the fall of Barad-dûr.
Angus McBride - Palantir of Osgiliath: The greatest of the seven stones stood in Osgiliath, the ancient capital of Gondor. For 1,500 years or more, it was held beneath the Dome of Stars that gave the city its name. The Stone of Osgiliath was so large it could not be lifted by a Man. During the early reign of Eldacar the Kin-strife arose. During this civil war, the city of Osgiliath was besieged and burned and the stone was lost in the waters of the river Anduin.
Principality of Dol Amroth by John Howe
By Clint Wilson. The stones were housed at Annúminas, Amon Sûl and Elostirion in Arnor and Osgiliath, Orthanc, Minas Ithil, and Minas Anor in Gondor. The Master-stone still resides in Tol Eressëa. Four of the stones are known to have been lost...The stone of Elostirion was taken back to Aman on the Ringbearers' ship. Only the stones of Minas Anor and Orthanc remain in Middle-earth, yet the stone of Minas Anor was marred, showing all but the most strong-willed the burning hands of Denethor…