Let's discuss power spikes

If you spend any time reading or watching aoe2 guides the term “power spike” will come up at some point. I’ve never seen this discussed in great detail, probably because the term itself is self-explanatory and people who are very familiar with the game know all the power spikes without having to think about them.

The more I play, the more I notice the importance of exploiting big power spikes (and within their window of opportunity they offer). So I’d like to discuss this in more detail, and ideally build some sort of reference guide of effective power spikes for different civilisations at different points in the game.

There are some very obvious ones, especially those spanning multiple civilisations that even noobs like me are very familiar with. Knights and Elite Eagle Warrior for instance are well known and common tactics are built around using their power spikes. Another obvious one is early gun powder units from Turks and Spanish.

What other units (or combinations of units) can be used for an effective spike in power to take control of the map and/or roll over enemy defences?