Vague Terminologies Describing Techeiles – Once in 70 Years

1. Swarms of shellfish may come up once in a very long time. The Radvaz states that this mass surfacing was a miraculous event that only occurred in the times of the Beis Hamikdash. After the Galus began, the Chilazon could only be obtained in its natural habitat – deep in the ocean.

1. The Romans had an event that occurred once every 70 years. R’ Benzion Halberstam in his video “Glimpse into the Mind of a Posek” adds that when the Romans had a certain event where a healthy Roman was riding on the shoulders of a crippled Jew (representing Yaakov who limped), this Jew needed to walk carrying the Roman around. It was meant to symbolize that the Romans were “on top” and the Jews were forever crippled. such that Esav was on top of Yaakov and the Romans were considered “Edom” like Esav was called. This event was meant to be a once-in-a-lifetime event. Once-in-a-lifetime may refer to 70 years because 70 years historically was used to describe the length of ones life. At this event the Chilazon surfaced in much greater numbers in order so that people could more readily sell the blue cloth to others at this event.

Once in 70 years means never. We see precedence in how halachically a Beis Din that sentences someone to death even once in 70 years is a murderous Beis Din. So it’s really a euphamism for it never happening in such a manner.

“…וכן ערך חלזון בספרו נר ערוך… וכן כתב במשנת יעקב (תצוה)… ד’עולה לשבעים שנה’ אינו אלא לומר שאינו מצוי אלא לפרקים, ולכן השמיטו הרמב״ם.”
English: “Ner Aruch and Mishnas Yaakov explain that ‘seventy years’ is only a figure of speech for rarity. Rambam omitted it because it isn’t a siman, only an explanation for scarcity.”
📖 Source: תגובה לקונטרס לחלזון במשנת הראשונים, עמ’ 8