Are all switches in a 4-way circuit the same?
Note - these remarks are from a North American perspective, but I believe switching is done the same way in Europe.

Switch terminology can be confusing but once you understand it, it is pretty simple.  

When there's just one switch controlling the lights, it's simple, just a plain switch, labelled ON in the up position, OFF in the down position.  Technically this plain switch is a single pole single throw (SPST) switch but that's not important, nobody uses that term for building wiring.  You turn the switch on, the lights turn on, turn the switch off, the lights turn off.  

When you have more than one switch, you want any switch to "toggle" the lights at any time - if they're on, flip any switch and they turn off;  if they're off, flip any switch and they turn on.  As you'd expect, in multi switch circuits, switches are not labelled ON or OFF.  

When there's two switches controlling the light, you use two three-way switches.  Flip either switch to toggle the lights.  The switches are called three way switches because they have three terminals to attach wires, not because there are three switches in the circuit.  (Technically a three-way switch is a single pole double throw switch (SPDT) switch but again that term isn't really used in building wiring in North America.  Everyone just calls them three-way switches.)  



The wires between the two three-way switches are referred to as "travelers" and the other wire is referred to as the "common."  The diagram shows the logical arrangement of the source power, the switches, and the load.  The physical routing of the wiring may be much different depending how things are laid out.  There are also some special purpose three way circuits that are wired a little differently.  

When there's three or more switches controlling the light, you use two three way switches and one or more four way switches.  Four way switches have four terminals.  A four way switch is a variant of a double pole double throw (DPDT) switch, but again that's not really important. 



Note that you can have as many four-way switches as you want between the two three-ways at the ends.  You don't use five-way switches for four lights.  The position of the terminals on the switches also varies - you have to check the instructions or markings on the switch to determine how the travelers are connected.