I made a patio out of 18" patio pavers about 5 years ago (maybe more
now). They still look like the day I put them in. Couple of things I
did.

1. Removed anywhere from 0-8 inches of earth, to rough grade the area
and bring it level with the existing house entry (sidewalk).
2. Added and rough graded anywhere from added approximately 6 inches
of lime rock (small pea sized gravel, with lime mixed in). I manually
tamped this several times and let it settle over about 2 months (other
projects going on as well).
3. I had placed framing around the area that intended to leave. This
was treated lumber. I then put approximately 1 inch of sand in and
graded this to an almost glass smooth finish. I had the whole thing
sloping away from the house approximately 1/4" per foot. I decided to
offset each row. So in other words, the first row, I had 1/2 a paver,
then full ones until the last one, which was the other 1/2. In the
next row I started with a full paver and ended with a full paver. The
next row was back to 1/2 first and last. On the next row, I went back
to full. A staggered pattern, I guess.. This really helped to lock in
the big pavers.
4. I manually tamped them in one last time (carefully) to help them
settle. And then spread sand between the joints. But the joints are
so tight, there is little sand going in between!
5. Finally, I took some of the dirt I dug out in the beginning and
graded the edges out from the framing.

As you can see...a WHOLE LOT of work! But it does hold up VERY well
and we spend many enjoyable hours on the deck.

By the way, I dug in 4 posts later and some framing on top of those
posts and added a tarp thing, that filters about 80% of the sun. Helps
keep it cool on those hot days.

Having said ALL that, you can just plop those things on the ground if
you want. But they will likely shift. I had a friend that did what
you are considering for a sidewalk and it works...and frankly, it
doesn't look to bad. But when he tries to shovel snow off it.....wow!
He's cussin'.