The antonyms for the phrase "was vertical" can differ depending on the context it is used in. In terms of posture, the opposite of being vertical is being horizontal, slouching, or leaning. When it comes to direction, the opposite of vertical is horizontal, diagonal, or slanting. In the case of buildings, the antonym for vertical would be horizontal or flat. However, alternative antonyms could be in reference to a state of emotion, such as feeling happy or content, or in the case of machinery, not functioning or broken. Therefore, the antonyms for "was vertical" are dependent on how the phrase is being used.