The silver arches are a ter'angreal made of of three connected arches. They are in the possession of the White Tower. The original purpose of the arches is unknown, but it is now used in the test to raise a novice to Accepted.
Inside the archesEdit
By passing through the arches, the entrant will become subject to her greatest fears of the past, present, and future in turn, passing through another of the arches for each. The One Power must be channeled into the arches at all times while a person is inside, or else they will become lost to the outside world forever, if they even survive.
When inside the arches, a person's greatest fears will be made real, presented as possibilities of what was, is, and what could be. The person loses nearly all knowledge that what they see is an illusion, and takes everything as reality, to an extent. It is unknown exactly how much hold the illusions bear on reality, but there is no doubt that they are at least loosely based off of the truth. It is also unclear where exactly the arches takes a person to face their fears.
The arch that the person entered reappears inside the illusion only once, and usually during the instance in which it is the most difficult for the person to leave what they see, either emotionally or physically. However, Nynaeve al'Meara managed to make the way out reappear a second time during her test by channeling.
Channeling itself is dangerous inside the arches, as studies of the ter'angreal have shown. Aes Sedai who have entered the arches holding the power or surrounded by wards have either emerged stilled or not at all. Those who channel and manage to return to reality are considered very fortunate.
A problem Edit
The Silver Arches seem to be related to Tel'aran'rhiod. When Egwene passes the test to become Accepted, she brings the twisted stone ring with her. The Silver Arches then create a buzz felt by the Aes Sedai channeling on it. When Egwene is in the Arches, she encounters some problems, especially during the third and last part.
Alanna Mosvani, a Green Sister operating the Arches during the test, said a reverberation came during the test. "The ter'angreal almost seemed to be trying to shut off the flow from saidar." Alanna then revelead that "the only time [she has] ever seen anything like it was once years ago when [she] tried to use a ter'angreal in the same room with another that may have been in some way related to it." Egwene knows that the only other ter'angreal in the room is the twisted stone ring she just received from Verin Mathwin.