Article: Following the Fourth Crusade and the fall of Constantinople to the "Latins" in 1204 mainland Greece was split between the Greek Despotate of Epirus (a Byzantine successor state) and Frankish rule (known as the Frankokratia), while some islands came under Venetian rule. The re-establishment of the Byzantine imperial capital in Constantinople in 1261 was accompanied by the empire's recovery of much of the Greek peninsula, although the Frankish Principality of Achaea in the Peloponnese and the rival Greek Despotate of Epirus in the north both remained important regional powers into the 14th century, while the islands remained largely under Genoese and Venetian control.

Now answer this question: In 1261 Constantinople was the capital for which empire?
Byzantine