Much of the centre of Paris was remodelled and rebuilt in the mid-19th Century, under the direction of Baron Haussmann, with new, wide boulevards and avenues sweeping through the city.
The first line of the Métro, Paris' underground railway, arrived in 1900. The Métro system now forms a dense network within the city boundaries. In the city of Paris, you are never more than 500 metres from a Métro station.
Although the Métro system provides comprehensive coverage of the city, and is very heavily-used, it is complemented by a network of bus routes. 60 routes operate within the city boundary, with around another 300 routes in the suburbs.
As is the case in most of the cities I have visited outside the UK, single-deck buses are used. Within the city boundary, all have been wheelchair-accessible since 2009.
On route maps, the bus routes are assigned different colours. These are repeated on the route number displays on the fronts of the buses, and in many cases on route informaiton boards carried on the sides of the vehicles.
The Roissybus service to Charles de Gaulle airport runs from Opéra in the centre of Paris; the Orlybus route starts from Denfert-Rochereau south of the city centre.
Double-deck buses can be found in Paris - but, as in many cities on the European mainland, they are only used on sightseeing tour work. As might be expected in such a major tourist destination, there are plenty of tour buses operated by two companies - l'Open Tour and les Cars Rouges. In some cities, second-hand double-deckers converted to open-top are used for sightseeing tours. Here in Paris, both companies use purpose-built open-toppers.
The district of Montmartre (literally, Martyr's Mount) overlooks the city centre. Crowned by the Basilica of Sacré Coeur, it is very popular with tourists.
The narrow, winding lanes preclude full-size buses from the Montmartre district. A dedicated bus route, "Montmartrobus", operates through the Montmartre using small buses. These connects the district with both the Métro and other bus routes nearby. The vehicles are in most cases battery-powered. Despite their small-size, they have two doors.
Although most of the buses on the Montmartrobus service are battery-powered, I did find one diesel-powered bus operating alongside them.
Montmartrobus isn't the only transport connection to Montmartre. There is also a funicular, first opened in 1900. It has since been modernised twice, most recently in 1991.
The streets on Montmartre are unsuitable for the sightseeing tour buses. A road train offers guided tours - commentaries are in French and English, but the website is in French only.
You won't find trams in the centre of Paris. Although a tram system had opened in the mid-19th Century, the last line closed in 1957. Nevertheless, there are trams operating now if you know where to look.
The Métro and suburban rail lines generally cater for radial journeys into, across and out of the city centre. Métro lines 2 and 6 form a ring around the centre of Paris, but the rail services do not provide easily for orbital journeys further out in the suburbs. Tram lines are being opened in stages to cater for some of the busier orbital suburban flows, with the first line opening in 1992. Paris' trams generally operate on segregated track.
In many European cities, main line railways converge on a single central station. Paris, however, is more like London in this respect, with a number of main line station forming a ring around the historic city centre.
Connections between the main line stations and from these stations into the heart of the city are provided by the Métro, and also by the RER (Réseau Express Régional) suburban rail services which operate across the city in tunnel. While the majority of the Métro is also in tunnel, there are also sections which emerge above ground particularly on Lines 2 and 6.
The transport system is co-ordinated by RATP (Régie Autonome des Transports Parisiens), who operate the bus, tram, funicular and Métro systems as well as part of the RER. RATP's commercial arm also owns the l'Open Tour sightseeing operation (and bus companies in London and Bournemouth amongst many other transport interests around the world). RATP is owned by the French state.
The fare system is reasonably simple. A flat fare applies to any journey by bus (except for Orlybus, Roissybus, sightseeing tours and a couple of other special services), tram, funicular, Métro, and also within an inner Zone on RER services. Transfers between buses or between bus and tram are allowed for up to 90 minutes, as are transfers between Métro and RER (within the inner Zone). However the single fare does not allow transfer from bus or tram to Métro or RER, or vice versa.
There are also anomalies where the Métro extends beyond the boundary of the inner Zone - for example to La Défense. La Défense is linked to the centre of Paris by both RER and Métro, but the flat fare ticket can only be used on the Métro. The RER charges different fares outside the inner Zone.
The single fare (apart from the exceptions described above) is currently €1.70. You can save money buy buying a "carnet" of 10 tickets for €13.30. You validate the tickets as you use them.