Civita Castellana was settled during the Iron Age by the Falisci, who called it Falerii. They were not Etruscans, but a distinct group, said to have been of Greek origin. They were culturally different from the Etruscans, but often their neighbors, allies and trading partners. Civita Castellana/Faleria was already important 3000 years ago, and was protected from invaders by its high position and surrounding stream and cliffs. The Romans defeated the Falisci in 396 BC and in again in 241 BC after a revolt by the locals who were then required to build a new, less defensible, city about 5 km away. This two was known as Falerii Novi (see Get Out). The original city was repopulated in the early Middle Ages because it offered greater protection, and it adopted the new name of Civita Castellana that was first mentioned in 994 AD. In the following centuries the city was a flourishing independent town with its own bishop.
There is only one DECENT book written about the under-appreciated area of Northern Lazio that is worth acquiring and reading prior to your trip or visit to the town of Civita Castellana (buy it used, from amazon.co.uk):
NORTHERN LAZIO: AN UNKNOWN LAND, by Wayland Kennet & Elizabeth Young. It features alphabetically arranged chapters on most of the towns in the province and it is a beautifully researched and written volume based upon experience and a love for this area. At the back of the book is an amazingly useful matrix rating each of the towns for sites of all periods worth visiting, as well as many other factors. Civita rates second only to Viterbo in their rankings of visit-worthiness. This book was published in the UK in 1990, and a year later in Italian. The Italian version is very difficult to find. Be mindful of the fact that the scope of this guide is historical/factual. It cannot pretend to be a great guide for painters. Kennet hardly rhapsodizes about views of the landscape. The best source for information for places and views to paint is in the paintings themselves that were executed in this area.
Civita Castellana is located about 60 kilometers north of Rome. By car from Rome’s ring road, the GRA, take the SS2bis (known as the Cassia bis or the Cassia Veientana) until Gabelletta/UMILTA' and then the SS311 in the direction of Nepi. Civita Castellana can also be reached by the Italian state railway from Tuburtina/Trastevere stations (not Stazione Termini) to Civita Castellana/Magliano Sabina. Locally this station is known as Borghetto for the frazione of Civita in which it is located. The local bus company, Vitertur, operates a service for commuters to the center of Civita. Tickets can be bought in either of the bars at that station for the sum of one euro. If the train is very late, you will have missed the bus. Ask fellow arriving passengers if they are driving to CC! They are often quite happy to give you a lift into town!
The MetRoma service from Piazzale Flaminio/Piazza del Popolo in Rome is limited to peak commuter travel hours and takes about 90 minutes to reach CC. The last half hour is stunningly beautiful but the trip overall is longer than it should be if the track were doubled or if the line had not been made to take the scenic route around Monte Soratte over 100 years ago. The local bus company, COTRAL, connects Saxa Rubra station to CC via the towns north of Rome along the Via Flaminia. Daily tickets cost €9 return (biglietto giornaliero) and can be used on the state railway, Cotral bus and the Metroma service (as well as all over in Rome if originating from CC). Arrive early and try to get on the car furthest from the train station. Single tickets for this train are a between 3 and 4 euros and can be bought at Piazzale Flaminio station.
There is a train that connects CC to Fiumicino airport directly without changing in Rome. It is a commuter train and crowded in peak hours, but you will always get a seat from the airport. The schedule is somewhat limited, and the train terminates in ORTE, two stops beyond CC. Cost of this ticket is 11 euros each way, tickets can be also be bought at the newspaper stand in the airport train station so don't waste time lining up at the ticket office if it is crowded. Be sure the destination indicted is ORTE, and not Fara Sabina an intermediate terminus of this service which will strand you in the middle of the Sabine Hills still very far from CC. Set an alarm - you will be tired after your trip and dozing off on that train is likely to result in missing your stop. Signs for stations are very difficult to read from inside the train and seldom announced. CC/Magliano Sabina is the stop right after COLLEVECCHIO!
Be careful not to take the Leonardo Express service from the train station at the airport by accident. It is faster, and more expensive, and only goes as far as Rome's main station, Stazione Termini. It is normally departing from the track (there are only two at this airport) on the right hand side, while the Orte-train normally departs from the track on the left. Check carefully before alighting.
Getting around is best accomplished on foot (for daily needs), or by car.
Getting to Rome
METROMA services Civita with the Roma-Viterbo trainline, which takes 90 minutes from Civita to Piazzale Flaminio/Piaaza del Popolo. A scenic, but slow route used by students and folks who work in Rome. Therefore there are many options very early in the morning (last departure from CC at about 8 a.m., then a gap in service to Rome until lunchtime, then return trains from Rome after school/work hours.
Here is a link to an undated schedule: 
Note that service is somewhat reduced in summer due to fewer students needing the train. Also note that festivo service is strictly Sunday and holidays. Day tickets from Civita Castellana are 9 euros, but this includes back and forth to Rome, as well as all buses, subways and trams around Rome. This daily ticket cannot be used to get all the way to Fiumicino airport.
Great local ceramics at the shop of Vincenzo Dobbolino (aka Mastro Cencio). His store is an Alladin's cave of skilled reproductions of classical wares - Etruscan, Greek, Faliscan, medieval, as well as his modern, original pieces. The shop is impossible to miss if coming from the main free parking lots as the result of a newly executed facade that looks like a giant version of a red-figure vase. Vincenzo is also knowledgeable about local topography, history, flora, fauna and hiking trails. He will lead you on a tour for a modest fee (to cover his expenses and time) and has a sunny and pleasant disposition. A true artisan and a gentleman.
Fausto Mancini: a talented local ceramicist and painter with a shop at the corner of the main piazza (Matteotti) and Via Garibaldi. Classical shapes and historically accurate glazes and colors.
Vine Idee - Piazza della Liberazione (new part of town): wine, lunch, dinner, pizza.
Civita suffers from a dearth of central, affordable accommodation.
The Relais Falisco  is a very nice example of this French chain's service, located in Via Don Minzoni, just 50 meters from the Duomo. It is situated in the renovated Palazzo Feroldi delle Rose and is air-conditioned and staffed by helpful receptionists who all speak English. Approximately forty rooms, both singles (seven) and doubles, include a breakfast buffet. The hotel has wifi as well as private parking for guests. They also have conference rooms for meetings or private courses.
The other "local" accommodation is well outside of town.
Civita Castellana has a rich history, and was for centuries one day's ride north from Rome along the Via Flaminia - a place to stop and change horses. Civita is a superb base from which to explore Northern Lazio (by car).It was also one of the first locations that drew outdoor painters in the 18th century, and many of the views they painted are still unspoiled today. The local building material is mainly tufa, and the region is full of tufa cliffs and gorges, Etruscan burials and wonderful small towns.
Most amenities are within easy waking distance here in the old center of this ancient town, historically the center of the Faliscan empire. The Faliscans were contemporaries of the Etruscans and Civita finally fell to the Romans in 241 BC. It is built on a naturally defensible bluff. Civita also has a wonderful Antonio da Sangallo fortress built around 1500, which was a Papal palace and then a prison, and now a museum displaying Faliscan and Roman relics, where there is a free music festival every July. There are wonderful things to see all over the region: Viterbo has one of the best preserved medieval centers in Europe and the Terme dei Papi bath complex, Sutri, Calcata, Nepi, the Via Amerina (an ancient road lined with burial chambers carved into the rock), Monster Park at Bomarzo, Villa Farnese at Caprarola, Villa Lante at Bagnaia, nearby Castel Sant'Elia with its 12th century Basilica and Sanctuary, the beech forest - La Faggeta - near Soriano, where the Romans came to capture wild animals for the sport in the Colisseum, also Amelia, Calvi, Otricoli, Lago di Bracciano, Lago di Vico, Faleri Novi, Oriolo Romano, Vignanello, Vasanello, San Martino al Cimino, Bolsena, Montefiascone, Tuscania, Civita di Bagnoregio. So many wonderful and uncrowded places to visit. It's a wonderful area to be based to see the wonderful Renaissance gardens of Lazio as well, and is near enough to the main A1 highway to allow day-trips to such places as Perugia, Orvieto, Todi, among others. Good coffee, food and wine and many festivals celebrating local food and traditions all summer long. Tuesdays and Fridays there is a smaller fresh fruit/vegetable market in the old part of town, and on Saturday mornings there is the big fresh market in the new part of town.
The best way to explore the area surrounding the town is on foot. There are superb trails down to and along the many rivers that have always defined this area. Descending into the surrounding woods is truly like stepping into the countryside as it was 3000 years ago. Local group Argilla (http://www.turismocivitacastellana.it) organizes excursions along these trails regularly, in cooperation with the Federtrek, for individuals and groups. The locals are friendly!