The phrase "was guard" can be replaced with a variety of synonyms depending on the context. Some alternatives could include "acted as a sentinel," "stood watch," "took charge of security," "served as a protector," and "maintained a vigil." Each of these phrases conveys the idea of someone or something being responsible for keeping a watchful eye over a particular area or person. Other possible synonyms could include "patrolled," "supervised," "monitored," "secured," or "watched over." Ultimately, the right synonym for "was guard" will depend on the specific circumstances and nuances of the situation being described.