Analysis reveals Glass Artifacts found in the Acropolis of Ialysos, Rhodes, a Century ago are 2,700-year-old Magnifying Lenses

A team of researchers from the Illinois State University, Western Illinois University, and the University of California at San Diego, conducted a detailed study of a set of artifacts discovered in the early 20th century by Italian archaeologists on the island of Rhodes, Greece.

These curious flat-convex glass objects mounted on bronze rings could be some of the earliest known examples of magnifying lenses from the ancient Mediterranean world. The discovery site was the archaeological site of the Temple of Athena in the acropolis of Ialysos, one of the three most important cities of Rhodes before 323 B.C.

It was here that in the 1920s and 1930s, an Italian archaeological mission excavated offering deposits in natural caves south and west of the temple, dating between 750-323 B.C.

Among the numerous recovered objects was a set of eight flat-convex glass artifacts surrounded by bronze rings with handles. Dating suggests that these objects came from deposits of the late Geometric period or early Archaic period (750-700 B.C.), based on other pieces found in the same context. This set stands out from other similar artifacts discovered in the eastern Mediterranean due to the unique presence of glass artifacts.

To determine their possible function, the team conducted a detailed optical analysis of the artifacts. They measured their focal lengths, which ranged between 18-21.5 mm, giving them theoretical magnifications of 8.3 to 13.2 times. They also tested their ability to resolve fine details in a resolution test chart and modern bills. Surprisingly, the best artifacts could discern details impossible to see with the naked eye.

Other evidence suggests that the artifacts were specifically designed to be mounted on rings. They have a protrusion that fits perfectly into the narrowest part of the bronze handle.

The marks on the handles seem to correlate with image quality, with better resolution artifacts having fewer marks. The researchers conclude that they indeed functioned as rudimentary magnifying lenses.

If they do date back to 750-700 B.C., they would be some of the earliest known magnifying lenses from the ancient world. This would have implications for understanding the development of optical technology and craftsmanship at the time. But who could have made them?

Given their sophisticated craftsmanship for the time, it is likely that Phoenician artisans with knowledge of glasswork, present in Rhodes and neighboring Aegean islands, were the creators. The Phoenicians were great sailors and traders who transmitted their knowledge to Mediterranean peoples. Due to its strategic location, Rhodes had significant development in glasswork during the Mycenaean period, which continued in later periods thanks to Phoenician influence.

It would not be unreasonable to think that Phoenician glassworkers and lapidaries based in Rhodes could have developed these early optical instruments. One may wonder for what purpose they would have been made.

Probably for use by artisans, such as seal or metal engravers, who needed to observe fine details. The modest magnification they provided would have already been an advantage over the naked eye. Thanks to them, crafts could have developed and perfected even further.

This discovery adds another piece to the puzzle of the origins of optics in antiquity. It demonstrates that at least in some more advanced Mediterranean cultures, rudimentary optical tools were known and manufactured before the Hellenistic period.

Sources

Georgia Tsouvala, Lee L. Brice, Alex Papen, George Papen, Quantitative characterization of archaic magnifying lenses from Ialysos, Rhodes. Journal of Archaeological Science: Reports, vol.53, February 2024, 104320. doi.org/10.1016/j.jasrep.2023.104320