Pact of Anwyn
"There will be times when the eldar will need allies to do things they cannot or which are forbidden to them. We have helped you in your hour of need. You must, when the time comes, help us." - words of the Farseer inscribed on the Byblos Belisarius.
The Pact of Anwyn is a secret treaty forged between the Ancient Navigator House Belisarius of Terra and the Eldar of Craftworld Ulthwe. It was formed by the year 101.M31 when House Belisarius's honour and wealth was somehow saved by the Eldar of Ulthwe. In gratitude for their help, an ancient treaty was forged with the creation of golden ducat trade coins crafted by the clan, with seven such coins traded to the Farseer by Jubal Belisarius. These coins remained within the Eldar as tokens that promised the House's support in order to repay any debt and which people of Ulthwe could call upon at any time. Those called upon under the pact took the Eldar wherever they wished to go as part of the friendship between the two sides. They were required to do anything within their means to accomplish the debt, though that did not necessarily ask for using property belonging to another to conduct such a goal.
Such was the secrecy of the treaty that some members of the House believed it to be a myth. Despite this being the case, safeguards were in place that ensured security of the ancient pact which involved revealing the golden ducat coin and speaking the exact words in the order that needed to be said both in Man's language as well as the Eldar tongue. By the 41st Millenium, at least five of the coins had been redeemed in the Belisarius family shrine located on Terra. The Farseer Auric Stormcloud of the line of Manan of World of Ulthwe invoked the Pact to Simon Belisarius, thus securing his aid in order to repay one of the seven debts of honour that exist between the House and the Craftworld.