Which alphabet, developed around 1500 BC, included only consonant sounds?

The Phoenician alphabet, developed around 1500 BC, is significant because it was one of the earliest alphabets to represent consonant sounds primarily, with vowels not being distinctly indicated in its characters. This innovation allowed for a more efficient method of writing compared to earlier systems, such as cuneiform, which was a complex system of symbols that represented both sounds and ideas.

The design of the Phoenician alphabet laid the groundwork for many subsequent alphabets, including Greek and Latin, by introducing a phonetic system that could be used for a wide range of languages with limited characters. By focusing on consonants, the Phoenician alphabet catered to the linguistic structures of its time, emphasizing consonantal roots, which are central to Semitic languages.

In contrast, the other options either refer to writing systems that included both consonants and vowels or formed later adaptations of existing systems. For instance, the Roman alphabet evolved from the Greek alphabet, which integrated a system that included both consonants and vowels. Thus, the unique characteristic of the Phoenician alphabet is its focus solely on consonant sounds, making it a pivotal development in the history of written language.