Sindered became Archbishop of Toledo in Visigothic Hispania around the year 710 or 711, succeeding Gunderic

Gunderic, Archbishop of Toledo

Gunderic was the Archbishop of Toledo briefly between Felix and Sindered from about 701. He was a Visigoth and is highly praised in the Chronicle of 754, according to which he was a holy man who performed many miracles...

. But at least one later chronicler makes him archbishop during the reign of Wittiza

Wittiza

Wittiza was the Visigothic King of Hispania from 694 until his death, co-ruling with his father, Ergica, until 702 or 703.-Joint rule:...

 (694–710), during which he supposedly took part in Wittiza's challenge to church authority during the last nine years of his reign. Sindered is said to have obeyed the king's orders "by continually harassing and persecuting men of high standing amongst the clergy" in the kingdom, though all that's reliably recorded is that, according to the Chronicle of 754

Chronicle of 754

The Chronicle of 754 was a Latin-language history in ninety-five chapters with the narrative theme "the ruin of Spain", which was composed in the year 754, in Toledo or Córdoba...

, either he or Gunderic instituted some sort of pressure.

Sources

• Bradley, Henry. The Goths: from the Earliest Times to the End of the Gothic Dominion in Spain. 2nd ed. New York: G. P. Putnam's Sons, 1883. (See chapter 34, pp. 355–357, in the Kessinger Publishing reprint, ISBN 1417970847.)
• Collins, Roger
  Roger Collins
  Roger J. H. Collins is an English medievalist, currently an honorary fellow in history at the University of Edinburgh.Collins studied at the University of Oxford under Peter Brown and John Michael Wallace-Hadrill. He then taught ancient and medieval history at the universities of Liverpool and...
  
  . "'Sicut lex Gothorum continet': Law and Charters in Ninth- and Tenth-Century León and Catalonia." The English Historical Review
  The English Historical Review
  The English Historical Review is an academic journal founded in 1886 and published by the Oxford University Press. It publishes articles on British, European, and World history since the classical era....
  
  , 100 (1985), 396, pp. 489–512.
• Collins, Roger
  Roger Collins
  Roger J. H. Collins is an English medievalist, currently an honorary fellow in history at the University of Edinburgh.Collins studied at the University of Oxford under Peter Brown and John Michael Wallace-Hadrill. He then taught ancient and medieval history at the universities of Liverpool and...
  
  . Visigothic Spain, 409–711. Blackwell Publishing, 2004.