Proto-Indo-Iranian, also Proto-Indo-Iranic is the reconstructed proto-language of the Indo-Iranian/Indo-Iranic branch of Indo-European. Its speakers, the hypothetical Proto-Indo-Iranians, are assumed to have lived in the late 3rd millennium BC, and are often connected with the Sintashta culture of the Eurasian Steppe and the early Andronovo archaeological horizon. Proto-Indo-Iranian was a satem language, likely removed less than a millennium from its ancestor, the late Proto-Indo-European language, and in turn removed less than a millennium from the Avestan and Vedic Sanskrit of the Rigveda, its descendants. Proto-Indo-Iranian has been considered to form a subgroup along with Greek, Armenian and Phrygian on the basis of many striking similarities in the morphological structure. However, this issue remains unsettled. It is the ancestor of the Indo-Aryan languages, the Iranian languages, and the Nuristani languages. Descriptive phonology In addition to the vowels, , and could function as the syllabic core. Two palatal series Proto-Indo-Iranian is hypothesized to have contained two series of stops or affricates in the palatal to postalveolar region. The phonetic nature of this contrast is not clear, and hence they are usually referred to as the primary or first series (*ć *ȷ́ *ȷ́ʰ (also represented as *ĉ, *ĵ, *ĵʰ), continuing Proto-Indo-European palatovelar *ḱ *ǵ *ǵʰ) and the second or secondary series (*č *ǰ *ǰʰ, continuing Proto-Indo-European plain and labialized velars, *k, *g, *gʰ and *kʷ, *gʷ, *gʷʰ, in palatalizing contexts). The following table shows the most common reflexes of the two series (Proto-Iranian is the hypothetical ancestor to the Iranian languages, including Avestan and Old Persian): Laryngeal Proto-Indo-European is usually hypothesized to have had three to four laryngeal consonants, each of which could occur in either syllabic or non-syllabic positions. In Proto-Indo-Iranian, the laryngeals merged as one phoneme /*H/. Beekes suggests that some instances of this /*H/ survived into Rigvedic Sanskrit and Avestan as unwritten glottal stops as evidenced by metrics. Accent Like Proto-Indo-European and Vedic Sanskrit (and also Avestan, though it was not written down), Proto-Indo-Iranian had a pitch accent system similar to present-day Japanese, conventionally indicated by an acute accent over the accented vowel. Historical phonology The most distinctive phonological change separating Proto-Indo-Iranian from Proto-Indo-European is the collapse of the ablauting vowels *e, *o into a single vowel, Proto-Indo-Iranian *a (but see Brugmann's law). Grassmann's law, Bartholomae's law, and the Ruki sound law were also complete in Proto-Indo-Iranian. A fuller list of some of the hypothesized sound changes from Proto-Indo-European to