Nero leaned forward against the ornate parapet, one hand up to shade his eyes.

"Don't squint so, dear," his young wife said. "Most unbecoming for an emperor."

He scowled. "They've gone all fuzzy again, way off over there. I can't see who is who!"

His wife snapped her finger, and a slave approached, bearing a small silver casket. "I knew this would happen again." She plucked up the lone gem lying on velvet. "A gift for you, my dear. Look through this." She handed her myopic husband a large translucent emerald, one facet cut concave.

Nero peered with one eye through the lens. "By Jupiter, there they are! As clear as the nose on my face! Where did you find this marvel?"

"All Rome knows how near-sighted you are, dear. Last time I visited the royal goldsmith, he said you should give this a try. He called it an ocularibus."

The crowd roared, and so did Nero. "Took him down at last, he did!" The paunchy emperor gestured high with his free arm, then gave the thumbs-down sign for the triumphant gladiator to decapitate his downed foe.

Nero's wife stifled a yawn as blood-thirsty cheers rang through the Colisseum.

Fast forward a dozen centuries...

Frau Schmidt left most of her entourage standing in the street as she stepped into the goldsmith's tiny shop.

"Guten dag!" the fellow greeted her. "How may I help you? You wish for new jewelry perhaps?" He uncovered a tray of rings and necklaces.

She waved a beringed hand at him. "No. I need one of those fancy beryl-circles. My cousin says they're such marvels, she can finally see her needlework again."

"Ah yes," the goldsmith said, producing another tray. "Lenses, my other specialty. Just the thing for aging eyes."

"I beg your pardon!" Frau Schmidt huffed.

"For the most delicate and sensitive of eyes, I mean."

Hardly appeased, his customer took her first look through a magnifying glass -- and gasped with delight. "It's true! These beryls are brilliant! I can see every line and wrinkle on the back of my hand! I'll take one. What do you call them?"

"Brillen, since they're made from beryl lenses."

Two hundred years later in the County of Tyrol...

Cardinal Nicholas of Cusa crumpled another precious sheet of paper and tossed it aside.

His sister, entering the study with a tray of pastries, glanced at the mess. "Your treatise not going well?" she asked.

"I need a metaphor," said the Bishop of Brixen. "To convey the concept of looking at philosophical matters both in detail and at a wide angle. Achieving the ability both to perceive and to comprehend. But every analogy I've tried falls flat."

"Looking, perceiving," she echoed. She pointed at one item on his desk, a gadget resembling scissors but bearing one lens in each arm. "How about your beryllos?"

Cusa brightened. "Brilliant idea, my dear! Yes indeed." He set to with pen and ink again, muttering aloud as he wrote. "'The beryl is a clear, bright, transparent stone, to which is given a concave as well as a convex form, and by looking through it, one attains what was previously invisible. If the intellectual beryl, which possesses both the maximum and the minimum in the same way, is adapted to the intellectual eyes, the indivisible principle of all things is attained...'" *

Meanwhile, in France:

"Marie, Marie," Grand-maman scolded. "Even I can tell your stitching is uneven. Hand me my beryl-circles and I'll see what needs fixing."

Marie giggled. "We don't call them that anymore! Maman says berycles, but the ladies at court all say 'besicles'."

Grand-maman sniffed. "When have you been at court?"

"I helped Auntie Adele fetch the mending."

"Adele! Adele, come here! What's this about court?"

Adele popped into the salon. "I told you I'd gotten the job, just last month. My word, your memory's as bad as your eyesight!"

Meanwhile, in Vatican City:

Giovanni Tortelli climbed up into the carriage, then took his valise from his valet. As the servant stepped away, the great man blurted out, "Wait! I've forgotten my spectacles. Fetch them at once."

"Your what, sir?"

"Spectacles. Spectacles! What you spectate with."

"Besicles?"

"Spectacles, besicles, whatever. Just go fetch them." The great man waved the fellow off, then drummed fingers until he returned. "To the library," Giovanni  ordered the driver.

Not just any library. The library of Pope Nicholas V where Giovanni Tortelli served as librarian.

And if the Pope's librarian referred to besicles as spectacles, then spectacles it was.

.

Detail of altarpiece depicting Saint Peter, by Nördlingen painter Friedrich Herlin; St. Jakob Church in Rothenburg ob der Tauber (Germany)

* ~ Cardinal Cusa (De beryllo, 1458, pages 4-5)

An emerald is a green beryl, colored by trace amounts of chromium. 

Ocularibus: term used by Plutarch.

Scissor-glasses: 15th century