I agree with everyone when they say the classical era is too short. Considering it entails from anywhere around 500BC to 500AD (or whatever you think it should be) it's too short. I think adding a few techs would help address the problem, but I think there is probably a better solution which makes more sense with regards to historical accuracy.
Make the techs for the classical era take longer to research! The classical era wasn't a time of technological inovation. At from what I've learned the romans and greeks never really but a lot of value into technology. Since they had so many slaves at the time there was no need to build better farming tools, or other time saving devices. Also the roman legions were fighting with the same weapons for almost the whole run of the empire. So really there isn't a lot of things to add in the first place. It makes sense to me to just draw out the era by making the techs to get into it, and out of it more expensive.
Make the techs for the classical era take longer to research! The classical era wasn't a time of technological inovation. At from what I've learned the romans and greeks never really but a lot of value into technology. Since they had so many slaves at the time there was no need to build better farming tools, or other time saving devices. Also the roman legions were fighting with the same weapons for almost the whole run of the empire. So really there isn't a lot of things to add in the first place. It makes sense to me to just draw out the era by making the techs to get into it, and out of it more expensive.