Formation of the Shard of Twelve Worlds

[["Information",[{"data":"[[Dark Age]]","label":"Era"},{"data":"c. 400 [[AR]]","label":"Date"},{"data":"Twelve planes of the [[Multiverse]]","label":"Location"},{"data":"''[[Ice Age]]''","label":"Sets"}]],["Outcome",[{"data":"\n*Prevention of [[Planeswalker (lore)|planeswalker]] travel into or out of the [[Shard of the Twelve Worlds]] until the end of the [[Ice Age (event)|Ice Age]]\n*Entrapment of several known planeswalkers, including [[Leshrac]], [[Tevesh Szat]], [[Freyalise]], [[Kristina of the Woods]], [[Taysir of Rabiah]] and [[Faralyn]] within the shard.\n*Conversely, [[Urza]] is locked out of the shard, barring him from returning to his home world."}]],["[[Timeline]]",[{"data":"[[Iwset-Jehesic War]]\n\n[[Formation of the Shard of Twelve Worlds|Formation of the Shard of Twelve Worlds]]\n[[Battle of Pitdown]]"}]]]

Formation of the Shard of Twelve Worlds
Information
Era	Dark Age
Date	c. 400 AR
Location	Twelve planes of the Multiverse
Sets	Ice Age
Outcome
Prevention of planeswalker travel into or out of the Shard of the Twelve Worlds until the end of the Ice Age Entrapment of several known planeswalkers, including Leshrac, Tevesh Szat, Freyalise, Kristina of the Woods, Taysir of Rabiah and Faralyn within the shard. Conversely, Urza is locked out of the shard, barring him from returning to his home world.
Timeline
Iwset-Jehesic War Formation of the Shard of Twelve Worlds Battle of Pitdown

The Formation of the Shard of Twelve Worlds was a silent but important event that occurred in the later part of the Dark Age on Terisiare, Dominaria.

Description

The Shard of the Twelve Worlds was an envelope containing twelve planes, separating them from the rest of the Multiverse. The only planes confirmed to be within the Shard were Dominaria, Azoria, and Ravidel's unnamed home plane. The Nether Void was accessible within the Shard, but whether it qualifies as a plane is unknown. Phyrexia was outside of the Shard.

The Shard was formed as a side-effect of the Sylex Blast. The blast bound several "nearby" planes together, forming the Dominarian Nexus, and also formed a barrier to travel in or out of the nexus. Many planeswalkers were trapped inside or locked out of the Shard during the Ice Age, including Leshrac, Tevesh Szat, Freyalise, Kristina of the Woods, Taysir of Rabiah and Faralyn within the shard, and Urza outside it. The plane of Shandalar drifts through the Multiverse in unusual ways, and it was thus able to pass through the boundary of the Shard, enabling trapped planeswalkers to access it. The later Summit of the Null Moon was held with this effect in mind.

Timing

Although the Shard did not finish forming until c. 400 AR, the process of closing off portals and direct access to Dominaria started soon after the Sylex Blast, effectively cutting Phyrexia off from Dominaria already in the earlier parts of the Dark Age.