Complex sentence: Walter, abbot of St Martin's, Laon, brought a colony of his canons and acted as their superior for nearly three years, until the canons, now in sufficient number, elected Simon, another canon of Laon, as their abbot.
Split into simpler sentences: Walter, Abbot of St Martin's, Laon, brought a colony of his canons and acted as their superior for nearly three years. The canons, now in sufficient number, elected Simon, a canon of Laon, as their abbot.