Background: Sonata Arctica is a Finnish power metal band from the town of Kemi, Finland. Created as a hard rock band named Tricky Beans, they later changed to Tricky Means and finally to Sonata Arctica, when they shifted to power metal. The current line-up consists of singer, keyboardist and songwriter Tony Kakko, guitarist Elias Viljanen, bass guitarist Pasi Kauppinen, keyboardist and keytarist Henrik Klingenberg, and drummer Tommy Portimo. All the musicians of the band's history except Portimo also acted as backing vocalists.
Context: On May 25, 2007, Unia was released. The album's first single, "Paid In Full", was released on April 27, 2007. On August 6, 2007, the band announced on their website that guitarist Jani Liimatainen had been asked to leave the band due to problems related to his conscription. He was replaced by Elias Viljanen who had already filled in for him in the band's Finnish and Japanese shows during the spring and summer.  In October 2007 Sonata Arctica headlined the ProgPower USA VIII. Later the band supported Nightwish across their 2008 tour of United States and Canada and headlined at the shows that Nightwish cancelled due to Anette Olzon's sudden severe sickness.  It was announced on September 4, 2008 that the band's first two albums would be re-released with bonus tracks by Spinefarm UK on October 6. The Days of Grays was released on September 16, 2009 in Finland and September 22 in the USA. Henrik stated that the new album would be in the same vein as Unia, but not as complex and darker. Singles from this album include "Flag in the Ground" and "The Last Amazing Grays". On August 28, 2009, the music video of "Flag In The Ground" was released to the web. The limited 2CD European edition of the album featured many of the album tracks with all instruments performed by a symphony orchestra.  The band also toured with DragonForce for the third U.S. leg of the Ultra Beatdown. In early 2010 they engaged on an Australian tour with Ensiferum and Melbourne band Vanishing Point. In April 2010, Sonata Arctica embarked on their USA and Canada Headlining tour for The Days of Grays. In October they headlined in Chile in support of the same album.
Question: When was Unia released?

Answer:
On May 25, 2007,