What words do you capitalize in the phrase old roman calendar?

You should capitalize "Roman" in the phrase "old Roman calendar".

Here's why:

* Proper Nouns: "Roman" refers to a specific civilization and culture, making it a proper noun. Proper nouns are always capitalized.

* Descriptive Words: "Old" and "calendar" are descriptive words and don't refer to a specific entity, so they are not capitalized.

Therefore, the correct capitalization is "old Roman calendar".