What form of poetry traditionally developed as letters and was popular in ancient times?

Epistolary poetry is indeed the correct answer because it refers to a form of poetry that is written in the style of letters. This type of poetry often addresses a specific person or group and conveys personal thoughts, emotions, or experiences in a manner similar to correspondence. It has roots in ancient literary traditions where poets would write poems that resemble letters, facilitating a direct conversation with the recipient or audience.

Other options reflect different genres of poetry. Ballads are narrative poems that tell stories, often focusing on themes of love, adventure, or tragedy, but they do not share the letter-like quality of being addressed to someone directly. Limericks are humorous five-line poems with a distinct rhythm and rhyme scheme, primarily intended for entertainment rather than personal communication. Picaresque poetry relates to a style that depicts the adventures of a roguish hero in an amusing way, which is not aligned with the characteristics of letter writing. Thus, epistolary poetry stands out as the unique form that aligns with the description of being traditional correspondence-like verses.