We learned in the Mishna:
And neither may a woman go out on to the public domain with a city of gold.
The Gemara asks:
What is the meaning of: With a city of gold? Rabba bar bar Ḥana said that Rabbi Yoḥanan said: Jerusalem of Gold, a gold tiara engraved with a depiction of the city of Jerusalem, like the one that Rabbi Akiva made for his wife.
Rabbi Akiva, who lived just after the destruction of the Second Temple, was one of the greatest of the tannaim. Unlettered until the age of 40, Akiva was encouraged by his wife Rachel to devote himself to the study of Torah. After years of study under the tutelage of Rabbi Eliezer ben Hyrcanus, Yehoshua ben Hanania and others, he returned with thousands of students and established his own academy in Bene Berak.
The “city of gold” ornament that Rabbi Akiva made for his wife is mentioned several times throughout the Talmud. The Gemara relates that when they lived in abject poverty they resided in a hayloft. When he saw that the hay got into his wife’s hair, Rabbi Akiva told her that if he ever became wealthy he would make her a “city of gold” ornament. Eventually, he kept his promise. In the Jerusalem Talmud, it is told that the wife of the Nasi, Rabban Shimon ben Gamliel, complained to him that she does not have so expensive an ornament. He asked her: Would you have done for me what Rabbi Akiva’s wife did for him? Rabbi Akiva’s wife sold the braids of her hair so that he could study Torah and she earned that ornament.
According to the descriptions of the Sages, the “city of gold” was a tiara on which the form of a city and its walls were depicted in gold. The Jerusalem of Gold specifically depicted the walls of Jerusalem. Apparently, this ornament was quite expensive and only a very limited number of aristocratic women wore it.