[Jim McDougall]

Oliver thank you so much for coming in on this!!Well noted on the fact that the place where a sword is found, whether intact, as a heirloom, trophy or as in this case, an excavated relic ...makes little difference as far as the origins of the item itself.

Going forward with research from various sources, I hope my interpretations might lend to some viable assessment of this example, and I always hope for corrections as required.

In this case, with the fact that this shamshir, clearly of Persian form and of course likely origin, was excavated from a local area after being in situ for an indeterminate period, in Zanzibar.

It is suggested that it would be likely that such a high quality sword might be expected to be found in Zanzibar as this was of course an Omani Sultanate, and with Omanis, as throughout the Dar al-Islam, the Persian shamshir was a highly prized mark of status.

With Zanzibar being a most dynamic entrepot for trade and diplomatic contact in East Africa linking the Red Sea, Gulf, and India with the Omani ports in Bahrain and Muscat being key in the network.
After the death of Said bin Sultan in Zanzibar in 1856, his dominions were split into two separate Sultanates based in MUSCAT and ZANZIBAR.

In Muscat, there was a resident population of Persian merchants who imported, assembled and exported arms into the interior, but certainly to Zanzibar as well.
(material taken from "Arms & Armor of Arabia in the 18th and 19th c", Robert Elgood, 1994, p.2, not quoted).

In looking at the example in discussion, the high relief calligraphy in the center of the cross guard reminded me of the use of the bold thuluth script as used decoratively in various Islamic situations. This pen (style) of Islamic calligraphy was popularized by Mehmed Sevki Efendi in the 19th c. but as written was also well known my Mustafah Rakira Efendi (1757-1826).
This is far out of my field, but the primary point here is that the inscription in the guard seems Thuluth, and Ottoman centered. Thuluth evolved with Ottoman calligrapher Hafiz Osman in the 17th century.

To be more specific, the thuluth style brought to mind the distinct blades which began being produced in Khorassan, Qazuin and Isfahan in response to increased demand for Persian blades both there and abroad in the late 18th early 19th century. These were heavier, with more complex system of fullers and grooves and with cartouche with pictogram of lion as well as large panel of this kind of calligraphy on other side of blade. These blades have been regarded as 'Persian revival' blades and from early to near mid 19th c.

These are shown and discussed in the outstanding article by Oliver Pinchot ("The Persian Shamshir and the Signature of Assad Allah", Arms Collecting, Vol.40, #1, 2002. p.7).
The reason for adding this is primarily for perspective.

With the demand for Persian blades demanding a shift to commercialism toward end of 18th c. , the impetus for likelihood of the example shamshir in discussion having a much earlier blade, probably more to middle of 18th century or earlier, and it being watered steel more likely as well.

With Persian blades, during the 17th century regular steel was used in roughly half the blades, while the majority of patterned steel blades had increased by end of century. Into the 18th virtually all Persian blades had complex and impressive patterns in the steel. The Persian damask blades were highly prized in Arabia, thus it would seem likely this example's blade is quite likely of some sort of damask.

Finally, I found a compellingly similar example in "At Study of the Eastern Sword", (Kirill Rivkin & Brian Isaac, 2017, example 178b):

From this, it is referred to as a QUALITY PERSIAN SHAMSHIR LATE 18TH CENTURY, with WOOTZ blade. Note inscriptions in cross guard. The cartouches on blade are as emulated in the later 'commercial' Persian blades with Lion of God pictogram.


The pics:
Top is often regarded as a Bedouin shamshir, however these, with the commercial Persian blades may occur throughout Arab spheres. These 'trade' blades from c.1800-40s are found in swords from Caucasian shashka, to Indian tulwars and many others. Shown as perspective with Persian shamshirs from end of 18th c.
Next:
The comparative example of Persian shamshir we are looking at, which appears from mid to latter 18th century, with likely earlier blade likely of watered steel, pattern unknown, and as of notable quality probably of some distinguished owner in Zanzibar. The corrosion of course makes further identification of blade difficult if not virtually impossible unless through radiographic analysis.
The missing grip plates, which were likely ivory, are in my opinion absent due to being removed for the ivory itself, and the sword likely stolen, was discarded accordingly.