Robot Entertainment and Microsoft have revealed more information about their upcoming entry in the Age of Empire franchise, including talk of a free-to-play business model. Age of Empires Online was first announced last summer and incorporates various MMO elements with the real-time strategy gameplay that earned AoE its popularity.

The game will launch later this year with Greek and Egyptian civilizations and PvP/co-op play. Unlike previous versions, AoE Online has a persistent system so civilizations develop and earn resources when you're not playing. You'll also be able to gain experience and equipment by questing and crafting – and that's where real money comes in.

Although much of the game will be free to everyone, players will be able to unlock additional content by purchasing a one-time Premium Civilization upgrade. In addition to special abilities and other perks, premium members gain access to "rare" and "epic" loot tiers, whereas non-paying users can only get "common" and "uncommon" items.

There are also plans for "booster" packs that let gamers buy new quests and gameplay types. Additionally, players will be able to customize the appearance of their civilization buy purchasing vanity items. The companies haven't released any information about how much the premium membership or microtransactions will cost.

People tend to get concerned about the balance of free-to-play games. Paying users sometimes gain an "unfair" advantage, which forces free players to lay down some cash if they want to be competitive. Microsoft's Ian Vogel recognized the issue in a comment on Gamasutra and said the company is paying close attention to balance.

"We're carefully looking at balance issues, and will be through the life of this product, and some of that will include how matchmaking works," said Vogel. "We don't want to nickel and dime you; we're trying to build a community. We're not just trying to sell you a product. We want to have something that's living and growing moving forward."