Tech trees started showing up in turn-based strategy games in the early 1990s[citation needed]. The 1991 video game Mega Lo Mania had a tech tree with a system of research levels/epochs that allowed the deployment of better units and defences and is considered to be the first game to combine a technology tree into a Real-time strategy game. The video game Civilization, also released in 1991, was probably the first turn-based strategy game to feature the same basic structure of tech trees seen in games today[citation needed].