The Battle of Grand Gulf was fought on April 29, 1863, during th: In the table, when obstruents (stops, affricates, and fricatives) appear in pairs, such as /p b/, /tʃ dʒ/, and /s z/, the first is fortis (strong) and the second is lenis (weak). Fortis obstruents, such as /p tʃ s/ are pronounced with more muscular tension and breath force than lenis consonants, such as /b dʒ z/, and are always voiceless. Lenis consonants are partly voiced at the beginning and end of utterances, and fully voiced between vowels. Fortis stops such as /p/ have additional articulatory or acoustic features in most dialects: they are aspirated [pʰ] when they occur alone at the beginning of a stressed syllable, often unaspirated in other cases, and often unreleased [p̚] or pre-glottalised [ʔp] at the end of a syllable. In a single-syllable word, a vowel before a fortis stop is shortened: thus nip has a noticeably shorter vowel (phonetically, but not phonemically) than nib [nɪˑb̥] (see below).[147]