Learn Italian: Il mosaico dell'altare di Santo Stefano è un gran mistero. - The mosaic of the altar of Saint Stephen is a great mystery.

The word santo changes form based on the first letter of the name that follows. Because Stefano starts with an s followed by a consonant, the full word Santo is used. If the name started with a vowel, it would be Sant', and for most other consonants, it drops the ending to become San.

Why does the sentence use gran mistero instead of grande mistero?

The adjective grande drops its final syllable to become gran when it is placed directly before a singular noun starting with a consonant. This is a phonetic shortcut called apocope that makes the phrase flow more smoothly in everyday speech.

Can I use gran if I place the adjective after the noun?

No, this type of shortening only happens when the adjective comes directly before the noun. If you place it after the noun, you must use the full form: un mistero grande. However, for phrases like un gran mistero, it sounds much more natural to keep the adjective before the noun.

Why do we use dell'altare rather than just di altare?