Greece:

Since the Kallikratis programme reform entered into effect on 1 January 2011, Greece has consisted of thirteen regions subdivided into a total of 325 municipalities. The 54 old prefectures and prefecture-level administrations have been largely retained as sub-units of the regions. Seven decentralized administrations group one to three regions for administrative purposes on a regional basis. There is also one autonomous area, Mount Athos (Greek: Agio Oros, "Holy Mountain"), which borders the region of Central Macedonia.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What went into effect on January 1, 2011?
Kallikratis programme reform