Going all the way back to Mycenean and even Minoan times, the Tree Sanctuary, or as I call it, the Pillar Complex, is one of the easiest and most beautiful outside constructions for ancient Greek rites. The picture on the left is of my own, built for my temple's sanctuary to host public rites. Walter Burkert, in his book Greek Religion, page 28, describes the architecture of this precinct.
"A large, imposing tree, almost always enclosed by a wall, and so set apart as sacred. The wall may be decorated with stucco or crowned with cult horns. A door, also embellished, leads into the interior, occasionally revealing a stone pillar. Various forms of altars are also shown, and in a number of cases a temple-like building stands opposite the tree. Open, stony ground is sometimes suggested."
My own Pillar Complex follows this basic pattern. It is built before a large tree, and the entire structure, including the tree, is encased by a brick wall (although in ancient times, the wall was probably much higher). The opening in the front leads into the interior where an altar and a stone pillar stands. The ground around it is also of small stones, but leaves in this picture are covering most of them up. The entire Complex is set apart from the rest of the surrounding area as its own sacred precinct. If you have your own property and are wanting to build religious structures, it's a far easier, more affordable alternative to a standing temple, which can take countless man hours, hard labor, and several thousands of dollars.
Building it out of stone and brick, and having it dominated by a strong tree, is in itself an excellent way to keep the structure standing and protected for a long period of time, and it will give you the ability to hold any kind of festival, rite or sacrifice to any God, Spirit, Hero, Ancestor or Deified Mortal the occasion calls for. In my own, the central pillar acts as a shrine, upon which a statue is placed of the One who is being worshiped at that time. So for a rite of Artemis, I'd place Her statue there during the rites. Of course, the Complex can also be a place for any time one wants to do general prayer and sacrifice. It doesn't have to always be one Deity at a time. Opposite the pillar, as you can see, is the altar, also made of stone and identified by being raised from the ground above the general flooring of the Complex. Upon the altar is also an incense burner to keep incense separate from things on the stone that might extinguish it, like libations or foods.
The first step is to find ground that is suitable. You want it to be as level as possible, otherwise the bricks you lay are all going to be crooked and it will drive you insane. You can also make the ground more level yourself by moving or adding soil. Making the ground proper and ready is a very crucial part, because ones those heavy bricks and stones are laid down, it's going to be very hard, if not impossible, to do anything about it unless you tear up the entire Complex and start over. So it is dire that you make sure the ground is good.
Step two is placing the flooring, which in mine is made of flat brick. The flooring is important because it's going to give the interior balance and stability. You notice that, for example, if you walk outside and just put a pillar on the bare ground, it's going to lean or fall over. Strong flooring helps against this. The brick used for the flooring also forms the altar on the far end toward the entrance by simply stacking themselves a few feet off the ground. The tree in the picture is encased by a wall of very simple red bricks, which are simply laid down and pressed into the soil where possible, all the way around the tree, pillar and altar, leaving a front entrance. Finally, gravel or stones fill the entire interior where the ground would still be visible. All together, the project took me an afternoon, and a cost of only about $60, since the only thing I had to buy was a stone pillar which I purchased at a local craft store, and the decorative flowers which were bought at a department store. Here's the best part, everything else was found around my home. By simply doing some scavenging, I found all the bricks and stones I needed. If you own your own house and land, there are probably more things lying around the yard and basement than you think, especially if you have just purchased the property.
On an ending note, when building an outside shrine, sanctuary or temple, if you can do so near a natural spring or natural water source, that would be the icing on the cake. Many temples and sanctuaries in ancient times followed the same custom, as the natural water can be used for purification of the sanctuary and the people entering it, and even as offerings to the Gods. If you've ever been to Circle Sanctuary in Wisconsin and looked at the springs of Brighid, those are natural springs.
On an ending note, when building an outside shrine, sanctuary or temple, if you can do so near a natural spring or natural water source, that would be the icing on the cake. Many temples and sanctuaries in ancient times followed the same custom, as the natural water can be used for purification of the sanctuary and the people entering it, and even as offerings to the Gods. If you've ever been to Circle Sanctuary in Wisconsin and looked at the springs of Brighid, those are natural springs.
In the Goodness of the Gods,
Chris Aldridge.