# How do you play “The Sentinel”?

Many, many years ago, we had a game for the Commodore 64 called "The Sentinel". I remember reading the instructions and being utterly baffled as to how you actually play the damned thing! Hopefully somebody remembers this game and can enlighten me...

The game displays a 3D playing field, divided up into squares. By pointing at a square, you can teleport to that square. (Takes forever to redraw the display!) The goal of the game, apparently, is to overlook the Sentinel and, by teleporting to his square, win the game...

...except that, by the laws of perspective, you can only ever overlook squares lower than you. But the Sentinel is always standing on the highest square on the map. How can you ever overlook the highest point on the map?!

To this day, several decades later, I'm still wondering how it's mathematically possible to win this game...

Stand at your desk. Look downward. Can you see your desk? If you were to teleport so that you were standing on top of it, would you be higher than you were before you teleported?

That said, the majority of height gains comes from the other gameplay element in The Sentinel — consuming and producing trees and boulders. Anything you consume gives you energy. You can spend energy on building boulders on a square you can see, to produce a higher surface to build a robot on.

So the primary challenge is to find a route through building and consuming that allows you to get higher than The Sentinel without ever being in his eyeline.

• And, as an aside, there's a Playstation-era sequel that's really more of a remake, and inevitably offers a much more approachable route in for new players. Teleportations are instant, besides anything else. – Tommy Feb 7 '20 at 20:50
• First paragraph of @Tommy 's answer explains this so well in a few short words; even I can comprehend it. – AndyF Feb 7 '20 at 22:39

One, the fact mentioned by others, that you only need to be higher than the surface of a square to be able to create a body and teleport there. The bodies have nonzero height, so you can gain one body-height for free. However, looking at some videos, I'm not sure if that's enough to go to a higher level. Here, at 2:04, it appears that the body created by the player is not tall enough to see the floor of the next-higher level. (That may depend on the version of the game, at least the remake Zenith is different in this.)

But, blocks can be used to go arbitrarily high, limited by energy. When the player creates blocks, they only need to see the side of a block to create a body or more blocks on top.

For example, in this video, at about 0:27, the player creates two blocks and a body, and it appears that the top of the second block is not visible. At 5:20, a similar thing is done, this time without even scrolling the view so that the top of the second block (and the body created there) would be visible. This also shows that they don't need to aim at the top of the block, only at the side. Similarly with three blocks in another video, at about 0:35.

The text on Wikipedia also appears to agree with this:

Controlling Synthoids that are standing at a higher level is fundamental to the game, because only the objects which occupy a visible square can be interacted with (the player may absorb or create objects on a boulder if the sides can be seen).

and

Height is gained by placing a boulder on any visible square, and putting a Synthoid on the boulder. The player may then transfer consciousness to the new Synthoid, and absorb the old one. Stacks of boulders of any height may be created, if the player has enough energy.

The energy required for creating blocks/boulders is of course acquired by absorbing trees (and sentries!) from the landscape, and reabsorbing blocks and bodies created by the player.

Both you and the sentinel have height. You just need to get high enough that your square plus your height is above the sentinel's square. You can absorb anything standing on a square you can see.

There were three types of elements: trees, cubes and Sentinels (1, 2, or 3 units of mass). So you could absorb e. g. 7 trees and build two cubes and an empty Sentinel on top of them. Then transfer your mind, absorb back the old Sentinel, and voila! - you are standing higher than before.

So the trees are the magic.

• Largely correct, but I think only the enemy was referred to as a. sentinel – Mark Williams Feb 8 '20 at 17:55
• @MarkWilliams Correct! You were in a robot (3 energy), and some levels had sentries (4 energy?) as well as the Sentinel (5 energy?). The 2 energy objects were called boulders. – CJ Dennis Feb 8 '20 at 23:03