Blood of Rome
In normal usage, a cellae is the main room of a pagan temple, the space that houses the statue of the god. In Necropolis, cella has a similar meaning, but with a twist. The Cellae of Necropolis enshrine Kindred as gods.
This does not mean that the Kindred declare themselves to be worthy of worship, at least not all the time. Rather they pick a god who embodies qualities they find admirable, and believe they themselves embody, and create a temple to that deity. The statue of the deity is then modelled after that kindred patron, and the deity given a qualifying title that refers to the Kindred. This is often an adjective derived from the vampires name.
These Cellae are used as temples by pagan Kindred, and most are well known; building a cella is an important part of establishing yourself as an important player in Kindred society. It is also a way for established kindred to take the measure of a newcomer, as anyone who starts by portraying himself as Jupiter is clearly a stuck-up parvenu with no taste. It is customary to start with lesser gods and work your way up.
Choosing a cella at which you worship is an important move in kindred politics, and something made public. This is normally done by leaving a small votive offering, traditionally silver, that identifies the offering kindred. Obviously worshiping at a temple associated with a Kindred shows support for that kindred, but for older vampires the choice of which temple to patronize also sends a message. Worshipping only at the cella a vampire established early during his requiem is subtly insulting, suggesting that he has achieved little or nothing since then.
+1 to +3 to intimidation rolls in your own cella, depending on how well made and patronized it is.