It's correct to say "a ruin". However, to speak about the remains of a city or building, the plural form, ruins, is more common.
It's correct to say "a ruin". However, to speak about the remains of a city or building, the plural form, ruins, is more common.
What's left of the building is just a ruin.
The ancient ruins of Troy are fascinating.
"Ruin" can also be an uncountable noun, which cannot be used with the article "a".
He is on the road to ruin.
When using "ruin" (singular) as a countable noun, include a determiner, such as "a", "the", or "this".
The recession in the US ended in the ruin of the service sector.
The plural form, ruins, requires a verb in the plural; for example, we say "ruins are" (not "ruins is")
The ruins are protected by the spirits of its priests.