After the earthquake, the town was in ruins.

was 是 be 动词的过去式，表示"是"或"处于某种状态"。 in 是介词，表示"处于某种状态或情况中"。 ruins 是名词 ruin 的复数形式，指"废墟、残骸"。 was in ruins 表示"处于废墟状态"，即"成为废墟"。