You always write a proper noun with a capital letter, since the noun represents the name of a specific person, place, or thing. The names of days of the week, months, historical documents, institutions, organizations, religions, their holy texts and their adherents are proper nouns. A proper noun is the opposite of a common noun
In each of the following sentences, the proper nouns are in bold:
The Marroons were transported from Jamaica and forced to build the fortifications in Halifax.
Many people dread Monday mornings.
Beltane is celebrated on the first of May.