The two following titles are conflated in the Sotheby 1898 catalogue as The seven great monarchies of the ancient eastern world. (Morris seems not to have owned The sixth great Oriental monarchy, published in 1873, or if he did, it may have been deaccessioned by the Wellcome Library, which has another copy without Morris’s book label.)
[1] Rawlinson, George. The five great monarchies of the ancient eastern world, or the history, geography, and antiquities of Chaldaea, Assyria, Babylon, Media, and Persia. 3rd ed. 3 vols. London: John Murray, 1873.
[2] Rawlinson. The seventh great Oriental monarchy, or the geography, history, and antiquities of the Sassanian or new Persian empire. 2 vols. in 1. London: Longmans, 1876.
Digital version: Internet Archive (Morris’s copy).
Provenance: Morris. — Richard Bennett. — Sotheby 1898, lot 822 (sold to Henry Wellcome for £6 10s.). — Henry Wellcome. — Wellcome Library (Closed stores Hist. 2 ZBB.28).
Reference: MS catalogue (2), no. 136 (where the title is rendered as “Rawlinson’s Ancient Monarchies”).
Sotheby 1898:
The Library of William Morris 
December 14, 2017
19th cent.